diff --git a/src/kdefrontend/dockwidgets/XYFitCurveDock.cpp b/src/kdefrontend/dockwidgets/XYFitCurveDock.cpp
index 98c319fc4..4e218a7ce 100644
--- a/src/kdefrontend/dockwidgets/XYFitCurveDock.cpp
+++ b/src/kdefrontend/dockwidgets/XYFitCurveDock.cpp
@@ -1,1403 +1,1414 @@
 /***************************************************************************
     File             : XYFitCurveDock.cpp
     Project          : LabPlot
     --------------------------------------------------------------------
     Copyright        : (C) 2014-2020 Alexander Semke (alexander.semke@web.de)
     Copyright        : (C) 2016-2020 Stefan Gerlach (stefan.gerlach@uni.kn)
     Description      : widget for editing properties of fit curves
 
  ***************************************************************************/
 
 /***************************************************************************
  *                                                                         *
  *  This program is free software; you can redistribute it and/or modify   *
  *  it under the terms of the GNU General Public License as published by   *
  *  the Free Software Foundation; either version 2 of the License, or      *
  *  (at your option) any later version.                                    *
  *                                                                         *
  *  This program is distributed in the hope that it will be useful,        *
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of         *
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the          *
  *  GNU General Public License for more details.                           *
  *                                                                         *
  *   You should have received a copy of the GNU General Public License     *
  *   along with this program; if not, write to the Free Software           *
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor,                    *
  *   Boston, MA  02110-1301  USA                                           *
  *                                                                         *
  ***************************************************************************/
 
 #include "XYFitCurveDock.h"
 #include "backend/core/AspectTreeModel.h"
 #include "backend/core/Project.h"
 #include "backend/lib/macros.h"
 #include "backend/gsl/ExpressionParser.h"
 #include "backend/worksheet/plots/cartesian/CartesianPlot.h"
 #include "commonfrontend/widgets/TreeViewComboBox.h"
 #include "kdefrontend/widgets/ConstantsWidget.h"
 #include "kdefrontend/widgets/FunctionsWidget.h"
 #include "kdefrontend/widgets/FitOptionsWidget.h"
 #include "kdefrontend/widgets/FitParametersWidget.h"
 
 #include <QMenu>
 #include <QWidgetAction>
 #include <QStandardItemModel>
 #include <QStandardPaths>
 #include <QClipboard>
 #include <QDir>
 
 extern "C" {
 #include "backend/nsl/nsl_sf_stats.h"
 }
 
 /*!
   \class XYFitCurveDock
   \brief  Provides a widget for editing the properties of the XYFitCurves
 		(2D-curves defined by a fit model) currently selected in
 		the project explorer.
 
   If more then one curves are set, the properties of the first column are shown.
   The changes of the properties are applied to all curves.
   The exclusions are the name, the comment and the datasets (columns) of
   the curves  - these properties can only be changed if there is only one single curve.
 
   \ingroup kdefrontend
 */
 
 XYFitCurveDock::XYFitCurveDock(QWidget* parent) : XYCurveDock(parent) {
 	//remove the tab "Error bars"
 	ui.tabWidget->removeTab(5);
 }
 
 /*!
  * 	set up "General" tab
  */
 void XYFitCurveDock::setupGeneral() {
 	DEBUG("XYFitCurveDock::setupGeneral()");
 	QWidget* generalTab = new QWidget(ui.tabGeneral);
 	uiGeneralTab.setupUi(generalTab);
 	m_leName = uiGeneralTab.leName;
 	m_leComment = uiGeneralTab.leComment;
 
 	auto* gridLayout = static_cast<QGridLayout*>(generalTab->layout());
 	gridLayout->setContentsMargins(2, 2, 2, 2);
 	gridLayout->setHorizontalSpacing(2);
 	gridLayout->setVerticalSpacing(2);
 
 	uiGeneralTab.cbDataSourceType->addItem(i18n("Spreadsheet"));
 	uiGeneralTab.cbDataSourceType->addItem(i18n("XY-Curve"));
 
 	cbDataSourceCurve = new TreeViewComboBox(generalTab);
 	gridLayout->addWidget(cbDataSourceCurve, 5, 3, 1, 4);
 
 	cbXDataColumn = new TreeViewComboBox(generalTab);
 	gridLayout->addWidget(cbXDataColumn, 6, 3, 1, 4);
 
 	cbXErrorColumn = new TreeViewComboBox(generalTab);
 	cbXErrorColumn->setEnabled(false);
 	uiGeneralTab.hlXError->addWidget(cbXErrorColumn);
 
 	cbYDataColumn = new TreeViewComboBox(generalTab);
 	gridLayout->addWidget(cbYDataColumn, 7, 3, 1, 4);
 
 	cbYErrorColumn = new TreeViewComboBox(generalTab);
 	cbYErrorColumn->setEnabled(false);
 	uiGeneralTab.hlYWeight->addWidget(cbYErrorColumn);
 
 	// X/Y-Weight
 	for (int i = 0; i < NSL_FIT_WEIGHT_TYPE_COUNT; i++) {
 		uiGeneralTab.cbXWeight->addItem(nsl_fit_weight_type_name[i]);
 		uiGeneralTab.cbYWeight->addItem(nsl_fit_weight_type_name[i]);
 	}
 	uiGeneralTab.cbXWeight->setCurrentIndex(nsl_fit_weight_no);
 	uiGeneralTab.cbYWeight->setCurrentIndex(nsl_fit_weight_no);
 
 	for (int i = 0; i < NSL_FIT_MODEL_CATEGORY_COUNT; i++)
 		uiGeneralTab.cbCategory->addItem(nsl_fit_model_category_name[i]);
 
 	uiGeneralTab.teEquation->setMaximumHeight(uiGeneralTab.leName->sizeHint().height() * 2);
 
 	fitParametersWidget = new FitParametersWidget(uiGeneralTab.frameParameters);
 	auto* l = new QVBoxLayout();
 	l->setContentsMargins(0, 0, 0, 0);
 	l->addWidget(fitParametersWidget);
 	uiGeneralTab.frameParameters->setLayout(l);
 
 	//use white background in the preview label
 	QPalette p;
 	p.setColor(QPalette::Window, Qt::white);
 	uiGeneralTab.lFuncPic->setAutoFillBackground(true);
 	uiGeneralTab.lFuncPic->setPalette(p);
 
 	uiGeneralTab.tbConstants->setIcon(QIcon::fromTheme("labplot-format-text-symbol"));
 	uiGeneralTab.tbFunctions->setIcon(QIcon::fromTheme("preferences-desktop-font"));
 	uiGeneralTab.pbRecalculate->setIcon(QIcon::fromTheme("run-build"));
 
 	// TODO: setting checked background color to unchecked color
 //	p = uiGeneralTab.lData->palette();
 	// QWidget::palette().color(QWidget::backgroundRole())
 	// not working with 'transparent'
 //	p.setColor(QPalette::Base, Qt::transparent);
 //	uiGeneralTab.lData->setPalette(p);
 	// see https://forum.qt.io/topic/41325/solved-background-of-checked-qpushbutton-with-stylesheet/2
 	// Styles not usable (here: text color not theme dependent). see https://forum.qt.io/topic/60546/qpushbutton-default-windows-style-sheet/9
 //	uiGeneralTab.lData->setStyleSheet("QToolButton:checked{background-color: transparent;border: 3px transparent;padding: 3px;}");
 
 //	uiGeneralTab.lData->setAutoFillBackground(true);
 
 	uiGeneralTab.twLog->setEditTriggers(QAbstractItemView::NoEditTriggers);
 	uiGeneralTab.twParameters->setEditTriggers(QAbstractItemView::NoEditTriggers);
 	uiGeneralTab.twGoodness->setEditTriggers(QAbstractItemView::NoEditTriggers);
 
 	//don't allow word wrapping in the log-table for the multi-line iterations string
 	uiGeneralTab.twLog->setWordWrap(false);
 
 	// show all options per default
 	showDataOptions(true);
 	showFitOptions(true);
 	showWeightsOptions(true);
 	showParameters(true);
 	showResults(true);
 
 	// context menus
 	uiGeneralTab.twParameters->setContextMenuPolicy(Qt::CustomContextMenu);
 	uiGeneralTab.twGoodness->setContextMenuPolicy(Qt::CustomContextMenu);
 	uiGeneralTab.twLog->setContextMenuPolicy(Qt::CustomContextMenu);
 	connect(uiGeneralTab.twParameters, &QTableWidget::customContextMenuRequested,
 			this, &XYFitCurveDock::resultParametersContextMenuRequest);
 	connect(uiGeneralTab.twGoodness, &QTableWidget::customContextMenuRequested,
 			this, &XYFitCurveDock::resultGoodnessContextMenuRequest);
 	connect(uiGeneralTab.twLog, &QTableWidget::customContextMenuRequested,
 			this, &XYFitCurveDock::resultLogContextMenuRequest);
 
 	uiGeneralTab.twLog->horizontalHeader()->resizeSections(QHeaderView::ResizeToContents);
 	uiGeneralTab.twGoodness->horizontalHeader()->resizeSections(QHeaderView::ResizeToContents);
 	uiGeneralTab.twGoodness->item(0, 1)->setText(UTF8_QSTRING("χ²"));
 	uiGeneralTab.twGoodness->item(1, 1)->setText(i18n("reduced") + ' ' + UTF8_QSTRING("χ²")
 		+ " (" + UTF8_QSTRING("χ²") + "/dof)");
 	uiGeneralTab.twGoodness->item(3, 1)->setText(UTF8_QSTRING("R²"));
 	uiGeneralTab.twGoodness->item(4, 1)->setText(UTF8_QSTRING("R̄²"));
 	uiGeneralTab.twGoodness->item(5, 0)->setText(UTF8_QSTRING("χ²") + ' ' + i18n("test"));
 	uiGeneralTab.twGoodness->item(5, 1)->setText("P > " + UTF8_QSTRING("χ²"));
 
 	auto* layout = new QHBoxLayout(ui.tabGeneral);
 	layout->setMargin(0);
 	layout->addWidget(generalTab);
 
 	//Slots
 	connect(uiGeneralTab.leName, &QLineEdit::textChanged, this, &XYFitCurveDock::nameChanged);
 	connect(uiGeneralTab.leComment, &QLineEdit::textChanged, this, &XYFitCurveDock::commentChanged);
 	connect(uiGeneralTab.chkVisible, &QCheckBox::clicked, this, &XYFitCurveDock::visibilityChanged);
 	connect(uiGeneralTab.cbDataSourceType, QOverload<int>::of(&QComboBox::currentIndexChanged), this, &XYFitCurveDock::dataSourceTypeChanged);
 	connect(uiGeneralTab.lWeights, &QPushButton::clicked, this, &XYFitCurveDock::showWeightsOptions);
 	connect(uiGeneralTab.cbXWeight, QOverload<int>::of(&QComboBox::currentIndexChanged), this, &XYFitCurveDock::xWeightChanged);
 	connect(uiGeneralTab.cbYWeight, QOverload<int>::of(&QComboBox::currentIndexChanged), this, &XYFitCurveDock::yWeightChanged);
 	connect(uiGeneralTab.cbCategory, QOverload<int>::of(&QComboBox::currentIndexChanged), this, &XYFitCurveDock::categoryChanged);
 	connect(uiGeneralTab.cbModel, QOverload<int>::of(&QComboBox::currentIndexChanged), this, &XYFitCurveDock::modelTypeChanged);
 	connect(uiGeneralTab.sbDegree, QOverload<int>::of(&QSpinBox::valueChanged), this, &XYFitCurveDock::updateModelEquation);
 	connect(uiGeneralTab.teEquation, &ExpressionTextEdit::expressionChanged, this, &XYFitCurveDock::expressionChanged);
 	connect(uiGeneralTab.tbConstants, &QToolButton::clicked, this, &XYFitCurveDock::showConstants);
 	connect(uiGeneralTab.tbFunctions, &QToolButton::clicked, this, &XYFitCurveDock::showFunctions);
 	connect(uiGeneralTab.pbOptions, &QPushButton::clicked, this, &XYFitCurveDock::showOptions);
 	connect(uiGeneralTab.pbRecalculate, &QPushButton::clicked, this, &XYFitCurveDock::recalculateClicked);
 	connect(uiGeneralTab.lData, &QPushButton::clicked, this, &XYFitCurveDock::showDataOptions);
 	connect(uiGeneralTab.lFit, &QPushButton::clicked, this, &XYFitCurveDock::showFitOptions);
 	connect(uiGeneralTab.lParameters, &QPushButton::clicked, this, &XYFitCurveDock::showParameters);
 	connect(uiGeneralTab.lResults, &QPushButton::clicked, this, &XYFitCurveDock::showResults);
 
 	connect(cbDataSourceCurve, &TreeViewComboBox::currentModelIndexChanged, this, &XYFitCurveDock::dataSourceCurveChanged);
 	connect(cbXDataColumn, &TreeViewComboBox::currentModelIndexChanged, this, &XYFitCurveDock::xDataColumnChanged);
 	connect(cbYDataColumn, &TreeViewComboBox::currentModelIndexChanged, this, &XYFitCurveDock::yDataColumnChanged);
 	connect(cbXErrorColumn, &TreeViewComboBox::currentModelIndexChanged, this, &XYFitCurveDock::xErrorColumnChanged);
 	connect(cbYErrorColumn, &TreeViewComboBox::currentModelIndexChanged, this, &XYFitCurveDock::yErrorColumnChanged);
 }
 
 /*
  * load curve settings
  */
 void XYFitCurveDock::initGeneralTab() {
 	DEBUG("XYFitCurveDock::initGeneralTab()");
 	//if there are more then one curve in the list, disable the tab "general"
 	if (m_curvesList.size() == 1) {
 		uiGeneralTab.lName->setEnabled(true);
 		uiGeneralTab.leName->setEnabled(true);
 		uiGeneralTab.lComment->setEnabled(true);
 		uiGeneralTab.leComment->setEnabled(true);
 
 		uiGeneralTab.leName->setText(m_curve->name());
 		uiGeneralTab.leComment->setText(m_curve->comment());
 	} else {
 		uiGeneralTab.lName->setEnabled(false);
 		uiGeneralTab.leName->setEnabled(false);
 		uiGeneralTab.lComment->setEnabled(false);
 		uiGeneralTab.leComment->setEnabled(false);
 
 		uiGeneralTab.leName->setText(QString());
 		uiGeneralTab.leComment->setText(QString());
 	}
 
 	auto* fitCurve = static_cast<XYFitCurve*>(m_curve);
 	checkColumnAvailability(cbXDataColumn, fitCurve->xDataColumn(), fitCurve->xDataColumnPath());
 	checkColumnAvailability(cbYDataColumn, fitCurve->yDataColumn(), fitCurve->yDataColumnPath());
 	checkColumnAvailability(cbXErrorColumn, fitCurve->xErrorColumn(), fitCurve->xErrorColumnPath());
 	checkColumnAvailability(cbYErrorColumn, fitCurve->yErrorColumn(), fitCurve->yErrorColumnPath());
 
 	uiGeneralTab.cbDataSourceType->setCurrentIndex(m_fitCurve->dataSourceType());
 	this->dataSourceTypeChanged(uiGeneralTab.cbDataSourceType->currentIndex());
 	XYCurveDock::setModelIndexFromAspect(cbDataSourceCurve, m_fitCurve->dataSourceCurve());
 	XYCurveDock::setModelIndexFromAspect(cbXDataColumn, m_fitCurve->xDataColumn());
 	XYCurveDock::setModelIndexFromAspect(cbYDataColumn, m_fitCurve->yDataColumn());
 	XYCurveDock::setModelIndexFromAspect(cbXErrorColumn, m_fitCurve->xErrorColumn());
 	XYCurveDock::setModelIndexFromAspect(cbYErrorColumn, m_fitCurve->yErrorColumn());
 
 	int tmpModelType = m_fitData.modelType;	// save type because it's reset when category changes
 	if (m_fitData.modelCategory == nsl_fit_model_custom)
 		uiGeneralTab.cbCategory->setCurrentIndex(uiGeneralTab.cbCategory->count() - 1);
 	else
 		uiGeneralTab.cbCategory->setCurrentIndex(m_fitData.modelCategory);
 	categoryChanged(m_fitData.modelCategory);	// fill model types
 
 	m_fitData.modelType = tmpModelType;
 	if (m_fitData.modelCategory != nsl_fit_model_custom)
 		uiGeneralTab.cbModel->setCurrentIndex(m_fitData.modelType);
 
 	uiGeneralTab.cbXWeight->setCurrentIndex(m_fitData.xWeightsType);
 	uiGeneralTab.cbYWeight->setCurrentIndex(m_fitData.yWeightsType);
 	uiGeneralTab.sbDegree->setValue(m_fitData.degree);
 
 	if (m_fitData.paramStartValues.size() > 0)
 		DEBUG("	start value 1 = " << m_fitData.paramStartValues.at(0));
 
 	DEBUG("	model degree = " << m_fitData.degree);
 
 	this->showFitResult();
 
 	uiGeneralTab.chkVisible->setChecked(m_curve->isVisible());
 
 	//Slots
 	connect(m_fitCurve, &XYFitCurve::aspectDescriptionChanged, this, &XYFitCurveDock::curveDescriptionChanged);
 	connect(m_fitCurve, &XYFitCurve::dataSourceTypeChanged, this, &XYFitCurveDock::curveDataSourceTypeChanged);
 	connect(m_fitCurve, &XYFitCurve::dataSourceCurveChanged, this, &XYFitCurveDock::curveDataSourceCurveChanged);
 	connect(m_fitCurve, &XYFitCurve::xDataColumnChanged, this, &XYFitCurveDock::curveXDataColumnChanged);
 	connect(m_fitCurve, &XYFitCurve::yDataColumnChanged, this, &XYFitCurveDock::curveYDataColumnChanged);
 	connect(m_fitCurve, &XYFitCurve::xErrorColumnChanged, this, &XYFitCurveDock::curveXErrorColumnChanged);
 	connect(m_fitCurve, &XYFitCurve::yErrorColumnChanged, this, &XYFitCurveDock::curveYErrorColumnChanged);
 	connect(m_fitCurve, &XYFitCurve::fitDataChanged, this, &XYFitCurveDock::curveFitDataChanged);
 	connect(m_fitCurve, &XYFitCurve::sourceDataChanged, this, &XYFitCurveDock::enableRecalculate);
 
 	connect(fitParametersWidget, &FitParametersWidget::parametersChanged, this, &XYFitCurveDock::parametersChanged);
 	connect(fitParametersWidget, &FitParametersWidget::parametersValid, this, &XYFitCurveDock::parametersValid);
 }
 
 void XYFitCurveDock::setModel() {
 	DEBUG("XYFitCurveDock::setModel()");
 	QList<AspectType> list{AspectType::Folder, AspectType::Datapicker, AspectType::Worksheet,
 	                       AspectType::CartesianPlot, AspectType::XYCurve};
 	cbDataSourceCurve->setTopLevelClasses(list);
 
 	QList<const AbstractAspect*> hiddenAspects;
 	for (auto* curve : m_curvesList)
 		hiddenAspects << curve;
 	cbDataSourceCurve->setHiddenAspects(hiddenAspects);
 
 	list = {AspectType::Folder, AspectType::Workbook, AspectType::Spreadsheet, AspectType::LiveDataSource,
 	        AspectType::Column, AspectType::CantorWorksheet, AspectType::Datapicker
 	       };
 	cbXDataColumn->setTopLevelClasses(list);
 	cbYDataColumn->setTopLevelClasses(list);
 	cbXErrorColumn->setTopLevelClasses(list);
 	cbYErrorColumn->setTopLevelClasses(list);
 
 	cbDataSourceCurve->setModel(m_aspectTreeModel);
 	cbXDataColumn->setModel(m_aspectTreeModel);
 	cbYDataColumn->setModel(m_aspectTreeModel);
 	cbXErrorColumn->setModel(m_aspectTreeModel);
 	cbYErrorColumn->setModel(m_aspectTreeModel);
 
 	XYCurveDock::setModel();
 }
 
 /*!
   sets the curves. The properties of the curves in the list \c list can be edited in this widget.
 */
 void XYFitCurveDock::setCurves(QList<XYCurve*> list) {
 	DEBUG("XYFitCurveDock::setCurves()");
 	m_initializing = true;
 	m_curvesList = list;
 	m_curve = list.first();
 	m_aspect = m_curve;
 	m_fitCurve = dynamic_cast<XYFitCurve*>(m_curve);
 	m_aspectTreeModel = new AspectTreeModel(m_curve->project());
 	this->setModel();
 	m_fitData = m_fitCurve->fitData();
 	if (m_fitData.paramStartValues.size() > 0) {
 		DEBUG("	start value 1 = " << m_fitData.paramStartValues.at(0));
 	}
 	DEBUG("	model degree = " << m_fitData.degree);
 	DEBUG("	# params = " << m_fitData.paramNames.size());
 	DEBUG("	# start values = " << m_fitData.paramStartValues.size());
 	fitParametersWidget->setFitData(&m_fitData);
 
 	initGeneralTab();
 	initTabs();
 	enableRecalculate();
 
 	m_initializing = false;
 
 	//init parameter list when not available
 	if (m_fitData.paramStartValues.size() == 0)
 		updateModelEquation();
 
 }
 
 //*************************************************************
 //**** SLOTs for changes triggered in XYFitCurveDock *****
 //*************************************************************
 void XYFitCurveDock::dataSourceTypeChanged(int index) {
 	const auto type = (XYAnalysisCurve::DataSourceType)index;
 	if (type == XYAnalysisCurve::DataSourceSpreadsheet) {
 		uiGeneralTab.lDataSourceCurve->hide();
 		cbDataSourceCurve->hide();
 		uiGeneralTab.lXColumn->show();
 		cbXDataColumn->show();
 		uiGeneralTab.lYColumn->show();
 		cbYDataColumn->show();
 	} else {
 		uiGeneralTab.lDataSourceCurve->show();
 		cbDataSourceCurve->show();
 		uiGeneralTab.lXColumn->hide();
 		cbXDataColumn->hide();
 		uiGeneralTab.lYColumn->hide();
 		cbYDataColumn->hide();
 	}
 
 	if (m_initializing)
 		return;
 
 	for (auto* curve : m_curvesList)
 		dynamic_cast<XYFitCurve*>(curve)->setDataSourceType(type);
 }
 
 void XYFitCurveDock::dataSourceCurveChanged(const QModelIndex& index) {
 	auto* aspect = static_cast<AbstractAspect*>(index.internalPointer());
 	auto* dataSourceCurve = dynamic_cast<XYCurve*>(aspect);
 
 	if (m_initializing)
 		return;
 
 	for (auto* curve : m_curvesList)
 		dynamic_cast<XYFitCurve*>(curve)->setDataSourceCurve(dataSourceCurve);
 }
 
 void XYFitCurveDock::xDataColumnChanged(const QModelIndex& index) {
 	if (m_initializing)
 		return;
 
 	auto* aspect = static_cast<AbstractAspect*>(index.internalPointer());
 	auto* column = dynamic_cast<AbstractColumn*>(aspect);
 
 	for (auto* curve : m_curvesList)
 		dynamic_cast<XYFitCurve*>(curve)->setXDataColumn(column);
 
 	// set model dependent start values from new data
 	XYFitCurve::initStartValues(m_fitData, m_curve);
 
 	cbXDataColumn->useCurrentIndexText(true);
 	cbXDataColumn->setInvalid(false);
 }
 
 void XYFitCurveDock::yDataColumnChanged(const QModelIndex& index) {
 	if (m_initializing)
 		return;
 
 	auto* aspect = static_cast<AbstractAspect*>(index.internalPointer());
 	auto* column = dynamic_cast<AbstractColumn*>(aspect);
 
 	for (auto* curve : m_curvesList)
 		dynamic_cast<XYFitCurve*>(curve)->setYDataColumn(column);
 
 	// set model dependent start values from new data
 	XYFitCurve::initStartValues(m_fitData, m_curve);
 
 	cbYDataColumn->useCurrentIndexText(true);
 	cbYDataColumn->setInvalid(false);
 }
 
 void XYFitCurveDock::xErrorColumnChanged(const QModelIndex& index) {
 	if (m_initializing)
 		return;
 
 	auto* aspect = static_cast<AbstractAspect*>(index.internalPointer());
 	auto* column = dynamic_cast<AbstractColumn*>(aspect);
 
 	for (auto* curve : m_curvesList)
 		dynamic_cast<XYFitCurve*>(curve)->setXErrorColumn(column);
 
 	cbXErrorColumn->useCurrentIndexText(true);
 	cbXErrorColumn->setInvalid(false);
 }
 
 void XYFitCurveDock::yErrorColumnChanged(const QModelIndex& index) {
 	if (m_initializing)
 		return;
 
 	auto* aspect = static_cast<AbstractAspect*>(index.internalPointer());
 	auto* column = dynamic_cast<AbstractColumn*>(aspect);
 
 	for (auto* curve : m_curvesList)
 		dynamic_cast<XYFitCurve*>(curve)->setYErrorColumn(column);
 
 	cbYErrorColumn->useCurrentIndexText(true);
 	cbYErrorColumn->setInvalid(false);
 }
 
 ///////////////////////// fold/unfold options //////////////////////////////////////////////////
 
 void XYFitCurveDock::showDataOptions(bool checked) {
 	if (checked) {
 		uiGeneralTab.lData->setIcon(QIcon::fromTheme("arrow-down"));
 		uiGeneralTab.lDataSourceType->show();
 		uiGeneralTab.cbDataSourceType->show();
 		// select options for current source type
 		dataSourceTypeChanged(uiGeneralTab.cbDataSourceType->currentIndex());
 	} else {
 		uiGeneralTab.lData->setIcon(QIcon::fromTheme("arrow-right"));
 		uiGeneralTab.lDataSourceType->hide();
 		uiGeneralTab.cbDataSourceType->hide();
 		uiGeneralTab.lXColumn->hide();
 		cbXDataColumn->hide();
 		uiGeneralTab.lYColumn->hide();
 		cbYDataColumn->hide();
 		uiGeneralTab.lDataSourceCurve->hide();
 		cbDataSourceCurve->hide();
 	}
 }
 
 void XYFitCurveDock::showWeightsOptions(bool checked) {
 	if (checked) {
 		uiGeneralTab.lWeights->setIcon(QIcon::fromTheme("arrow-down"));
 		uiGeneralTab.lXWeight->show();
 		uiGeneralTab.cbXWeight->show();
 		uiGeneralTab.lXErrorCol->show();
 		cbXErrorColumn->show();
 		uiGeneralTab.lYWeight->show();
 		uiGeneralTab.cbYWeight->show();
 		uiGeneralTab.lYErrorCol->show();
 		cbYErrorColumn->show();
 	} else {
 		uiGeneralTab.lWeights->setIcon(QIcon::fromTheme("arrow-right"));
 		uiGeneralTab.lXWeight->hide();
 		uiGeneralTab.cbXWeight->hide();
 		uiGeneralTab.lXErrorCol->hide();
 		cbXErrorColumn->hide();
 		uiGeneralTab.lYWeight->hide();
 		uiGeneralTab.cbYWeight->hide();
 		uiGeneralTab.lYErrorCol->hide();
 		cbYErrorColumn->hide();
 	}
 }
 
 void XYFitCurveDock::showFitOptions(bool checked) {
 	if (checked) {
 		uiGeneralTab.lFit->setIcon(QIcon::fromTheme("arrow-down"));
 		uiGeneralTab.lCategory->show();
 		uiGeneralTab.cbCategory->show();
 		uiGeneralTab.lModel->show();
 		uiGeneralTab.cbModel->show();
 		uiGeneralTab.lEquation->show();
 
 		m_initializing = true;	// do not change start parameter
 		modelTypeChanged(uiGeneralTab.cbModel->currentIndex());
 		m_initializing = false;
 	} else {
 		uiGeneralTab.lFit->setIcon(QIcon::fromTheme("arrow-right"));
 		uiGeneralTab.lCategory->hide();
 		uiGeneralTab.cbCategory->hide();
 		uiGeneralTab.lModel->hide();
 		uiGeneralTab.cbModel->hide();
 		uiGeneralTab.lDegree->hide();
 		uiGeneralTab.sbDegree->hide();
 		uiGeneralTab.lEquation->hide();
 		uiGeneralTab.lFuncPic->hide();
 		uiGeneralTab.teEquation->hide();
 		uiGeneralTab.tbFunctions->hide();
 		uiGeneralTab.tbConstants->hide();
 	}
 }
 
 void XYFitCurveDock::showParameters(bool checked) {
 	if (checked) {
 		uiGeneralTab.lParameters->setIcon(QIcon::fromTheme("arrow-down"));
 		uiGeneralTab.frameParameters->show();
 	} else {
 		uiGeneralTab.lParameters->setIcon(QIcon::fromTheme("arrow-right"));
 		uiGeneralTab.frameParameters->hide();
 	}
 }
 
 void XYFitCurveDock::showResults(bool checked) {
 	if (checked) {
 		uiGeneralTab.lResults->setIcon(QIcon::fromTheme("arrow-down"));
 		uiGeneralTab.twResults->show();
 	} else {
 		uiGeneralTab.lResults->setIcon(QIcon::fromTheme("arrow-right"));
 		uiGeneralTab.twResults->hide();
 	}
 }
 
 ///////////////////////////////////////////////////////////////////////////
 
 void XYFitCurveDock::xWeightChanged(int index) {
 	DEBUG("xWeightChanged() weight = " << nsl_fit_weight_type_name[index]);
 
 	m_fitData.xWeightsType = (nsl_fit_weight_type)index;
 
 	// enable/disable weight column
 	switch ((nsl_fit_weight_type)index) {
 	case nsl_fit_weight_no:
 	case nsl_fit_weight_statistical:
 	case nsl_fit_weight_statistical_fit:
 	case nsl_fit_weight_relative:
 	case nsl_fit_weight_relative_fit:
 		cbXErrorColumn->setEnabled(false);
 		uiGeneralTab.lXErrorCol->setEnabled(false);
 		break;
 	case nsl_fit_weight_instrumental:
 	case nsl_fit_weight_direct:
 	case nsl_fit_weight_inverse:
 		cbXErrorColumn->setEnabled(true);
 		uiGeneralTab.lXErrorCol->setEnabled(true);
 		break;
 	}
 	enableRecalculate();
 }
 
 void XYFitCurveDock::yWeightChanged(int index) {
 	DEBUG("yWeightChanged() weight = " << nsl_fit_weight_type_name[index]);
 
 	m_fitData.yWeightsType = (nsl_fit_weight_type)index;
 
 	// enable/disable weight column
 	switch ((nsl_fit_weight_type)index) {
 	case nsl_fit_weight_no:
 	case nsl_fit_weight_statistical:
 	case nsl_fit_weight_statistical_fit:
 	case nsl_fit_weight_relative:
 	case nsl_fit_weight_relative_fit:
 		cbYErrorColumn->setEnabled(false);
 		uiGeneralTab.lYErrorCol->setEnabled(false);
 		break;
 	case nsl_fit_weight_instrumental:
 	case nsl_fit_weight_direct:
 	case nsl_fit_weight_inverse:
 		cbYErrorColumn->setEnabled(true);
 		uiGeneralTab.lYErrorCol->setEnabled(true);
 		break;
 	}
 	enableRecalculate();
 }
 
 /*!
  * called when the fit model category (basic functions, peak functions etc.) was changed.
  * In the combobox for the model type shows the model types for the current category \index and calls \c modelTypeChanged()
  * to update the model type dependent widgets in the general-tab.
  */
 void XYFitCurveDock::categoryChanged(int index) {
 	if (index == nsl_fit_model_custom) {
 		DEBUG("categoryChanged() category = \"nsl_fit_model_custom\"");
 	} else {
 		DEBUG("categoryChanged() category = \"" << nsl_fit_model_category_name[index] << "\"");
 	}
 
 	bool hasChanged = true;
 	// nothing has changed when ...
 	if (m_fitData.modelCategory == (nsl_fit_model_category)index || (m_fitData.modelCategory == nsl_fit_model_custom && index == uiGeneralTab.cbCategory->count() - 1) )
 		hasChanged = false;
 
 	if (uiGeneralTab.cbCategory->currentIndex() == uiGeneralTab.cbCategory->count() - 1)
 		m_fitData.modelCategory = nsl_fit_model_custom;
 	else
 		m_fitData.modelCategory = (nsl_fit_model_category)index;
 
 	uiGeneralTab.cbModel->clear();
 	uiGeneralTab.cbModel->show();
 	uiGeneralTab.lModel->show();
 
 	switch (m_fitData.modelCategory) {
 	case nsl_fit_model_basic:
 		for (int i = 0; i < NSL_FIT_MODEL_BASIC_COUNT; i++)
 			uiGeneralTab.cbModel->addItem(nsl_fit_model_basic_name[i]);
 		break;
 	case nsl_fit_model_peak: {
 		for (int i = 0; i < NSL_FIT_MODEL_PEAK_COUNT; i++)
 			uiGeneralTab.cbModel->addItem(nsl_fit_model_peak_name[i]);
 #if defined(_MSC_VER)
 		// disable voigt model
 		const QStandardItemModel* model = qobject_cast<const QStandardItemModel*>(uiGeneralTab.cbModel->model());
 		QStandardItem* item = model->item(nsl_fit_model_voigt);
 		item->setFlags(item->flags() & ~(Qt::ItemIsSelectable|Qt::ItemIsEnabled));
 #endif
 		break;
 	}
 	case nsl_fit_model_growth:
 		for (int i = 0; i < NSL_FIT_MODEL_GROWTH_COUNT; i++)
 			uiGeneralTab.cbModel->addItem(nsl_fit_model_growth_name[i]);
 		break;
 	case nsl_fit_model_distribution: {
 		for (int i = 0; i < NSL_SF_STATS_DISTRIBUTION_COUNT; i++)
 			uiGeneralTab.cbModel->addItem(nsl_sf_stats_distribution_name[i]);
 
 		// not-used items are disabled here
 		const auto* model = qobject_cast<const QStandardItemModel*>(uiGeneralTab.cbModel->model());
 
 		for (int i = 1; i < NSL_SF_STATS_DISTRIBUTION_COUNT; i++) {
 			// unused distributions
 			if (i == nsl_sf_stats_levy_alpha_stable || i == nsl_sf_stats_levy_skew_alpha_stable || i == nsl_sf_stats_bernoulli) {
 					QStandardItem* item = model->item(i);
 					item->setFlags(item->flags() & ~(Qt::ItemIsSelectable|Qt::ItemIsEnabled));
 			}
 		}
 		break;
 	}
 	case nsl_fit_model_custom:
 		uiGeneralTab.cbModel->addItem(i18n("Custom"));
 		uiGeneralTab.cbModel->hide();
 		uiGeneralTab.lModel->hide();
 	}
 
 	if (hasChanged) {
 		//show the fit-model for the currently selected default (first) fit-model
 		uiGeneralTab.cbModel->setCurrentIndex(0);
 		uiGeneralTab.sbDegree->setValue(1);
 		// when model type does not change, call it here
 		updateModelEquation();
 	}
 
 	enableRecalculate();
 }
 
 /*!
  * called when the fit model type (depends on category) was changed.
  * Updates the model type dependent widgets in the general-tab and calls \c updateModelEquation() to update the preview pixmap.
  */
 void XYFitCurveDock::modelTypeChanged(int index) {
 	DEBUG("modelTypeChanged() type = " << (unsigned int)index << ", initializing = " << m_initializing << ", current type = " << m_fitData.modelType);
 	// leave if there is no selection
 	if (index == -1)
 		return;
 
 	bool custom = false;
 	if (m_fitData.modelCategory == nsl_fit_model_custom)
 		custom = true;
 	uiGeneralTab.teEquation->setReadOnly(!custom);
 	uiGeneralTab.lModel->setVisible(!custom);
 	uiGeneralTab.cbModel->setVisible(!custom);
 	uiGeneralTab.tbFunctions->setVisible(custom);
 	uiGeneralTab.tbConstants->setVisible(custom);
 
 	// default settings
 	uiGeneralTab.lDegree->setText(i18n("Degree:"));
 	if (m_fitData.modelType != index)
 		uiGeneralTab.sbDegree->setValue(1);
 
 	auto* aspect = static_cast<AbstractAspect*>(cbXDataColumn->currentModelIndex().internalPointer());
 	auto* xColumn = dynamic_cast<AbstractColumn*>(aspect);
 	int availableRowCount = (xColumn != nullptr) ? xColumn->availableRowCount() : 0;
 	DEBUG(" available row count = " << availableRowCount)
 
+	bool disableFit = false;
 	switch (m_fitData.modelCategory) {
 	case nsl_fit_model_basic:
 		switch (index) {
 		case nsl_fit_model_polynomial:
 			uiGeneralTab.lDegree->setVisible(true);
 			uiGeneralTab.sbDegree->setVisible(true);
 			uiGeneralTab.sbDegree->setMaximum(qMin(availableRowCount - 1, 10));
 			break;
 		case nsl_fit_model_fourier:
-			uiGeneralTab.lDegree->setVisible(true);
-			uiGeneralTab.sbDegree->setVisible(true);
-			uiGeneralTab.sbDegree->setMaximum(10);
-			//TODO: limit degree
+			if (availableRowCount < 4) {	// too few data points
+				uiGeneralTab.lDegree->setVisible(false);
+				uiGeneralTab.sbDegree->setVisible(false);
+				disableFit = true;
+			} else {
+				uiGeneralTab.lDegree->setVisible(true);
+				uiGeneralTab.sbDegree->setVisible(true);
+				uiGeneralTab.sbDegree->setMaximum(qMin(availableRowCount/2 - 1, 10));
+			}
 			break;
 		case nsl_fit_model_power:
 			uiGeneralTab.lDegree->setVisible(true);
 			uiGeneralTab.sbDegree->setVisible(true);
 			uiGeneralTab.sbDegree->setMaximum(2);
+			//TODO: limit degree depending on availableRowCount
 			break;
 		case nsl_fit_model_exponential:
 			uiGeneralTab.lDegree->setVisible(true);
 			uiGeneralTab.sbDegree->setVisible(true);
 			uiGeneralTab.sbDegree->setMaximum(10);
+			//TODO: limit degree depending on availableRowCount
 			break;
 		default:
 			uiGeneralTab.lDegree->setVisible(false);
 			uiGeneralTab.sbDegree->setVisible(false);
 		}
 		break;
 	case nsl_fit_model_peak:	// all models support multiple peaks
 		uiGeneralTab.lDegree->setText(i18n("Number of peaks:"));
 		uiGeneralTab.lDegree->setVisible(true);
 		uiGeneralTab.sbDegree->setVisible(true);
 		uiGeneralTab.sbDegree->setMaximum(9);
 		break;
 	case nsl_fit_model_growth:
 	case nsl_fit_model_distribution:
 	case nsl_fit_model_custom:
 		uiGeneralTab.lDegree->setVisible(false);
 		uiGeneralTab.sbDegree->setVisible(false);
 	}
 
 	m_fitData.modelType = index;
 
 	updateModelEquation();
+
+	if (disableFit)
+		uiGeneralTab.pbRecalculate->setEnabled(false);
 }
 
 /*!
  * Show the preview pixmap of the fit model expression for the current model category and type.
  * Called when the model type or the degree of the model were changed.
  */
 void XYFitCurveDock::updateModelEquation() {
 
 	if (m_fitData.modelCategory == nsl_fit_model_custom) {
 		DEBUG("XYFitCurveDock::updateModelEquation() category = nsl_fit_model_custom, type = " << m_fitData.modelType);
 	} else {
 		DEBUG("XYFitCurveDock::updateModelEquation() category = " << nsl_fit_model_category_name[m_fitData.modelCategory] << ", type = " << m_fitData.modelType);
 	}
 
 	//this function can also be called when the value for the degree was changed -> update the fit data structure
 	int degree = uiGeneralTab.sbDegree->value();
 	if (!m_initializing) {
 		m_fitData.degree = degree;
 		XYFitCurve::initFitData(m_fitData);
 		// set model dependent start values from curve data
 		XYFitCurve::initStartValues(m_fitData, m_curve);
 		// udpate parameter widget
 		fitParametersWidget->setFitData(&m_fitData);
 	}
 
 	// variables/parameter that are known
 	QStringList vars = {"x"};
 	vars << m_fitData.paramNames;
 	uiGeneralTab.teEquation->setVariables(vars);
 
 	// set formula picture
 	uiGeneralTab.lEquation->setText(QLatin1String("f(x) ="));
 	QString file;
 	switch (m_fitData.modelCategory) {
 	case nsl_fit_model_basic: {
 		// formula pic depends on degree
 		QString numSuffix = QString::number(degree);
 		if (degree > 4)
 			numSuffix = '4';
 		if ((nsl_fit_model_type_basic)m_fitData.modelType == nsl_fit_model_power && degree > 2)
 			numSuffix = '2';
 		file = QStandardPaths::locate(QStandardPaths::AppDataLocation, "pics/fit_models/"
 			+ QString(nsl_fit_model_basic_pic_name[m_fitData.modelType]) + numSuffix + ".png");
 		break;
 	}
 	case nsl_fit_model_peak: {
 		// formula pic depends on number of peaks
 		QString numSuffix = QString::number(degree);
 		if (degree > 4)
 			numSuffix = '4';
 		file = QStandardPaths::locate(QStandardPaths::AppDataLocation, "pics/fit_models/"
 			+ QString(nsl_fit_model_peak_pic_name[m_fitData.modelType]) + numSuffix + ".png");
 		break;
 	}
 	case nsl_fit_model_growth:
 		file = QStandardPaths::locate(QStandardPaths::AppDataLocation, "pics/fit_models/"
 			+ QString(nsl_fit_model_growth_pic_name[m_fitData.modelType]) + ".png");
 		break;
 	case nsl_fit_model_distribution:
 		file = QStandardPaths::locate(QStandardPaths::AppDataLocation, "pics/gsl_distributions/"
 			+ QString(nsl_sf_stats_distribution_pic_name[m_fitData.modelType]) + ".png");
 		// change label
 		if (m_fitData.modelType == nsl_sf_stats_poisson)
 			uiGeneralTab.lEquation->setText(QLatin1String("f(k)/A ="));
 		else
 			uiGeneralTab.lEquation->setText(QLatin1String("f(x)/A ="));
 		break;
 	case nsl_fit_model_custom:
 		uiGeneralTab.lFuncPic->hide();
 		uiGeneralTab.teEquation->show();
 		uiGeneralTab.teEquation->setPlainText(m_fitData.model);
 	}
 
 	if (m_fitData.modelCategory != nsl_fit_model_custom) {
 		DEBUG("Model pixmap path = " << STDSTRING(file));
 		uiGeneralTab.lFuncPic->setPixmap(file);
 		uiGeneralTab.lFuncPic->show();
 		uiGeneralTab.teEquation->hide();
 	}
 
 	enableRecalculate();
 }
 
 void XYFitCurveDock::showConstants() {
 	QMenu menu;
 	ConstantsWidget constants(&menu);
 
 	connect(&constants, &ConstantsWidget::constantSelected, this, &XYFitCurveDock::insertConstant);
 	connect(&constants, &ConstantsWidget::constantSelected, &menu, &QMenu::close);
 	connect(&constants, &ConstantsWidget::canceled, &menu, &QMenu::close);
 
 	auto* widgetAction = new QWidgetAction(this);
 	widgetAction->setDefaultWidget(&constants);
 	menu.addAction(widgetAction);
 
 	QPoint pos(-menu.sizeHint().width() + uiGeneralTab.tbConstants->width(), -menu.sizeHint().height());
 	menu.exec(uiGeneralTab.tbConstants->mapToGlobal(pos));
 }
 
 void XYFitCurveDock::showFunctions() {
 	QMenu menu;
 	FunctionsWidget functions(&menu);
 	connect(&functions, &FunctionsWidget::functionSelected, this, &XYFitCurveDock::insertFunction);
 	connect(&functions, &FunctionsWidget::functionSelected, &menu, &QMenu::close);
 	connect(&functions, &FunctionsWidget::canceled, &menu, &QMenu::close);
 
 	auto* widgetAction = new QWidgetAction(this);
 	widgetAction->setDefaultWidget(&functions);
 	menu.addAction(widgetAction);
 
 	QPoint pos(-menu.sizeHint().width() + uiGeneralTab.tbFunctions->width(), -menu.sizeHint().height());
 	menu.exec(uiGeneralTab.tbFunctions->mapToGlobal(pos));
 }
 
 /*!
  * Update parameter by parsing expression
  * Only called for custom fit model
  */
 void XYFitCurveDock::updateParameterList() {
 	DEBUG("XYFitCurveDock::updateParameterList()");
 	// use current model function
 	m_fitData.model = uiGeneralTab.teEquation->toPlainText();
 
 	ExpressionParser* parser = ExpressionParser::getInstance();
 	QStringList vars; // variables that are known
 	vars << "x";	//TODO: others?
 	m_fitData.paramNames = m_fitData.paramNamesUtf8 = parser->getParameter(m_fitData.model, vars);
 
 	// if number of parameter changed
 	int oldNumberOfParameter = m_fitData.paramStartValues.size();
 	int numberOfParameter = m_fitData.paramNames.size();
 	DEBUG(" old number of parameter: " << oldNumberOfParameter << " new number of parameter: " << numberOfParameter);
 	if (numberOfParameter != oldNumberOfParameter) {
 		m_fitData.paramStartValues.resize(numberOfParameter);
 		m_fitData.paramFixed.resize(numberOfParameter);
 		m_fitData.paramLowerLimits.resize(numberOfParameter);
 		m_fitData.paramUpperLimits.resize(numberOfParameter);
 	}
 	if (numberOfParameter > oldNumberOfParameter) {
 		for (int i = oldNumberOfParameter; i < numberOfParameter; ++i) {
 			m_fitData.paramStartValues[i] = 1.0;
 			m_fitData.paramFixed[i] = false;
 			m_fitData.paramLowerLimits[i] = -std::numeric_limits<double>::max();
 			m_fitData.paramUpperLimits[i] = std::numeric_limits<double>::max();
 		}
 	}
 
 	parametersChanged();
 }
 
 /*!
  * called when parameter names and/or start values for the model were changed
  * also called from parameter widget
  */
 void XYFitCurveDock::parametersChanged(bool updateParameterWidget) {
 	DEBUG("XYFitCurveDock::parametersChanged() m_initializing = " << m_initializing);
 
 	//parameter names were (probably) changed -> set the new names in EquationTextEdit
 	uiGeneralTab.teEquation->setVariables(m_fitData.paramNames);
 
 	if (m_initializing)
 		return;
 
 	if (updateParameterWidget)
 		fitParametersWidget->setFitData(&m_fitData);
 
 	enableRecalculate();
 }
 void XYFitCurveDock::parametersValid(bool valid) {
 	DEBUG("XYFitCurveDock::parametersValid() valid = " << valid);
 	m_parametersValid = valid;
 }
 
 void XYFitCurveDock::showOptions() {
 	QMenu menu;
 	FitOptionsWidget w(&menu, &m_fitData, m_fitCurve);
 	connect(&w, &FitOptionsWidget::finished, &menu, &QMenu::close);
 	connect(&w, &FitOptionsWidget::optionsChanged, this, &XYFitCurveDock::enableRecalculate);
 
 	auto* widgetAction = new QWidgetAction(this);
 	widgetAction->setDefaultWidget(&w);
 	menu.addAction(widgetAction);
 	menu.setTearOffEnabled(true);
 
 	//menu.setWindowFlags(menu.windowFlags() & Qt::MSWindowsFixedSizeDialogHint);
 
 	QPoint pos(-menu.sizeHint().width() + uiGeneralTab.pbOptions->width(), 0);
 	menu.exec(uiGeneralTab.pbOptions->mapToGlobal(pos));
 }
 
 void XYFitCurveDock::insertFunction(const QString& str) const {
 	//TODO: not all function have only one argument!
 	uiGeneralTab.teEquation->insertPlainText(str + "(x)");
 }
 
 void XYFitCurveDock::insertConstant(const QString& str) const {
 	uiGeneralTab.teEquation->insertPlainText(str);
 }
 
 /*!
  * When a custom evaluate range is specified, set the plot range too.
  */
 void XYFitCurveDock::setPlotXRange() {
 	if (m_fitData.autoEvalRange || m_curve == nullptr)
 		return;
 
 	auto* plot = dynamic_cast<CartesianPlot*>(m_curve->parentAspect());
 	if (plot != nullptr) {
 		double rmin = m_fitData.evalRange.first();
 		double rmax = m_fitData.evalRange.last();
 		double extend = (rmax-rmin) * 0.05;	// +/- 5 percent of range. may be < 0
 		if (extend != 0.) {	// avoid zero range
 			plot->setXMin(rmin - extend);
 			plot->setXMax(rmax + extend);
 		}
 	}
 }
 
 void XYFitCurveDock::recalculateClicked() {
 	DEBUG("XYFitCurveDock::recalculateClicked()");
 	QApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
 	m_fitData.degree = uiGeneralTab.sbDegree->value();
 	if (m_fitData.modelCategory == nsl_fit_model_custom)
 		updateParameterList();
 
 	for (XYCurve* curve: m_curvesList)
 		dynamic_cast<XYFitCurve*>(curve)->setFitData(m_fitData);
 
 	m_fitCurve->recalculate();
 	setPlotXRange();
 
 	//update fitParametersWidget
 	if (m_fitData.useResults) {
 		DEBUG(" nr of param names = " << m_fitData.paramNames.size())
 		DEBUG("	size of start values = " << m_fitData.paramStartValues.size())
 		DEBUG("	size of param values = " << m_fitCurve->fitResult().paramValues.size())
 		if (m_fitCurve->fitResult().paramValues.size() > 0) {	// may be 0 if fit fails
 			for (int i = 0; i < m_fitData.paramNames.size(); i++)
 				m_fitData.paramStartValues[i] = m_fitCurve->fitResult().paramValues.at(i);
 			fitParametersWidget->setFitData(&m_fitData);
 		} else {
 			DEBUG(" WARNING: no fit result available!")
 		}
 	}
 
 	this->showFitResult();
 
 	uiGeneralTab.pbRecalculate->setEnabled(false);
 	emit info(i18n("Fit status: %1", m_fitCurve->fitResult().status));
 	QApplication::restoreOverrideCursor();
 	DEBUG("XYFitCurveDock::recalculateClicked() DONE");
 }
 
 void XYFitCurveDock::expressionChanged() {
 	DEBUG("XYFitCurveDock::expressionChanged()");
 	if (m_initializing)
 		return;
 
 	// update parameter list for custom model
 	if (m_fitData.modelCategory == nsl_fit_model_custom)
 		updateParameterList();
 
 	enableRecalculate();
 }
 
 void XYFitCurveDock::enableRecalculate() {
 	DEBUG("XYFitCurveDock::enableRecalculate()");
 	if (m_initializing || m_fitCurve == nullptr)
 		return;
 
 	//no fitting possible without the x- and y-data
 	bool hasSourceData = false;
 	if (m_fitCurve->dataSourceType() == XYAnalysisCurve::DataSourceSpreadsheet) {
 		auto* aspectX = static_cast<AbstractAspect*>(cbXDataColumn->currentModelIndex().internalPointer());
 		auto* aspectY = static_cast<AbstractAspect*>(cbYDataColumn->currentModelIndex().internalPointer());
 		hasSourceData = (aspectX != nullptr && aspectY != nullptr);
 		if (aspectX) {
 			cbXDataColumn->useCurrentIndexText(true);
 			cbXDataColumn->setInvalid(false);
 		}
 		if (aspectY) {
 			cbYDataColumn->useCurrentIndexText(true);
 			cbYDataColumn->setInvalid(false);
 		}
 	} else {
 		hasSourceData = (m_fitCurve->dataSourceCurve() != nullptr);
 	}
 
 	uiGeneralTab.pbRecalculate->setEnabled(hasSourceData && m_parametersValid);
 
 	// PREVIEW as soon as recalculate is enabled (does not need source data)
 	if (m_parametersValid && m_fitData.previewEnabled) {
 		DEBUG("	EVALUATE WITH PREVIEW ENABLED");
 		// use recent fit data
 		m_fitCurve->setFitData(m_fitData);
 		// calculate fit function
 		m_fitCurve->evaluate(true);
 		setPlotXRange();
 	}
 	else {
 		DEBUG("	PREVIEW DISABLED");
 	}
 }
 
 void XYFitCurveDock::resultCopySelection() {
 	QTableWidget* tw{nullptr};
 	int currentTab = uiGeneralTab.twResults->currentIndex();
 	DEBUG("current tab = " << currentTab);
 	if (currentTab == 0)
 		tw = uiGeneralTab.twParameters;
 	else if (currentTab == 1)
 		tw = uiGeneralTab.twGoodness;
 	else if (currentTab == 2)
 		tw = uiGeneralTab.twLog;
 	else
 		return;
 
 	const QTableWidgetSelectionRange& range = tw->selectedRanges().constFirst();
 	QString str;
 	for (int i = 0; i < range.rowCount(); ++i) {
 		if (i > 0)
 			str += '\n';
 		for (int j = 0; j < range.columnCount(); ++j) {
 			if (j > 0)
 				str += '\t';
 			str += tw->item(range.topRow() + i, range.leftColumn() + j)->text();
 		}
 	}
 	str += '\n';
 	QApplication::clipboard()->setText(str);
 	DEBUG(STDSTRING(QApplication::clipboard()->text()));
 }
 
 void XYFitCurveDock::resultCopyAll() {
 	const XYFitCurve::FitResult& fitResult = m_fitCurve->fitResult();
 	int currentTab = uiGeneralTab.twResults->currentIndex();
 	QString str;
 	if (currentTab == 0) {
 		str = i18n("Parameters:") + '\n';
 
 		const int np = fitResult.paramValues.size();
 		for (int i = 0; i < np; i++) {
 			if (m_fitData.paramFixed.at(i))
 				str += m_fitData.paramNamesUtf8.at(i) + QString(" = ") + QString::number(fitResult.paramValues.at(i)) + '\n';
 			else {
 				str += m_fitData.paramNamesUtf8.at(i) + QString(" = ") + QString::number(fitResult.paramValues.at(i))
 					+ UTF8_QSTRING("±") + QString::number(fitResult.errorValues.at(i))
 					+ " (" + QString::number(100.*fitResult.errorValues.at(i)/std::abs(fitResult.paramValues.at(i)), 'g', 3) + " %)\n";
 
 				const double margin = fitResult.tdist_marginValues.at(i);
 				QString tdistValueString;
 				if (fitResult.tdist_tValues.at(i) < std::numeric_limits<double>::max())
 					tdistValueString = QString::number(fitResult.tdist_tValues.at(i), 'g', 3);
 				else
 					tdistValueString = UTF8_QSTRING("∞");
 				str += " (" + i18n("t statistic:") + ' ' + tdistValueString + ", "
 					+ i18n("p value:") + ' ' + QString::number(fitResult.tdist_pValues.at(i), 'g', 3) + ", "
 					+ i18n("conf. interval:") + ' ';
 				if (std::abs(fitResult.tdist_tValues.at(i)) < 1.e6) {
 					str += QString::number(fitResult.paramValues.at(i) - margin) + " .. "
 						+ QString::number(fitResult.paramValues.at(i) + margin) + ")\n";
 				} else {
 					str += i18n("too small");
 				}
 			}
 		}
 	} else if (currentTab == 1) {
 		str = i18n("Goodness of fit:") + '\n';
 		str += i18n("sum of squared residuals") + " (" + UTF8_QSTRING("χ²") + "): " + QString::number(fitResult.sse) + '\n';
 		if (fitResult.dof != 0) {
 			str += i18n("reduced") + ' ' + UTF8_QSTRING("χ²") + ": " + QString::number(fitResult.rms) + '\n';
 			str += i18n("root mean square error") + " (RMSE): " + QString::number(fitResult.rsd) + '\n';
 			str += i18n("coefficient of determination") + " (" + UTF8_QSTRING("R²") + "): " + QString::number(fitResult.rsquare, 'g', 15) + '\n';
 			str += i18n("adj. coefficient of determination")+ " (" + UTF8_QSTRING("R̄²")
 				+ "): " + QString::number(fitResult.rsquareAdj, 'g', 15) + "\n\n";
 
 			str += i18n("P > ") + UTF8_QSTRING("χ²") + ": " + QString::number(fitResult.chisq_p, 'g', 3) + '\n';
 			str += i18n("F statistic") + ": " + QString::number(fitResult.fdist_F, 'g', 3) + '\n';
 			str += i18n("P > F") + ": " + QString::number(fitResult.fdist_p, 'g', 3) + '\n';
 		}
 		str += i18n("mean absolute error:") + ' ' + QString::number(fitResult.mae) + '\n';
 		str += i18n("Akaike information criterion:") + ' ' + QString::number(fitResult.aic) + '\n';
 		str += i18n("Bayesian information criterion:") + ' ' + QString::number(fitResult.bic) + '\n';
 	} else if (currentTab == 2) {
 		str = i18n("status:") + ' ' + fitResult.status + '\n';
 		str += i18n("iterations:") + ' ' + QString::number(fitResult.iterations) + '\n';
 		str += i18n("tolerance:") + ' ' + QString::number(m_fitData.eps) + '\n';
 		if (fitResult.elapsedTime > 1000)
 			str += i18n("calculation time: %1 s", fitResult.elapsedTime/1000) + '\n';
 		else
 			str += i18n("calculation time: %1 ms", fitResult.elapsedTime) + '\n';
 		str += i18n("degrees of freedom:") + ' ' + QString::number(fitResult.dof) + '\n';
 		str += i18n("number of parameters:") + ' ' + QString::number(fitResult.paramValues.size()) + '\n';
 		str += i18n("fit range:") + ' ' + QString::number(m_fitData.fitRange.first()) + " .. " + QString::number(m_fitData.fitRange.last()) + '\n';
 
 		str += i18n("Iterations:") + '\n';
 		for (const auto &s : m_fitData.paramNamesUtf8)
 			str += s + '\t';
 		str += UTF8_QSTRING("χ²");
 
 		const QStringList iterations = fitResult.solverOutput.split(';');
 		for (const auto &s : iterations)
 			if (!s.isEmpty())
 				str += '\n' + s;
 	}
 
 	QApplication::clipboard()->setText(str);
 	DEBUG(STDSTRING(QApplication::clipboard()->text()));
 }
 
 void XYFitCurveDock::resultParametersContextMenuRequest(QPoint pos) {
 	auto* contextMenu = new QMenu;
 	contextMenu->addAction(i18n("Copy Selection"), this, &XYFitCurveDock::resultCopySelection);
 	contextMenu->addAction(i18n("Copy All"), this, &XYFitCurveDock::resultCopyAll);
 	contextMenu->exec(uiGeneralTab.twParameters->mapToGlobal(pos));
 }
 void XYFitCurveDock::resultGoodnessContextMenuRequest(QPoint pos) {
 	auto* contextMenu = new QMenu;
 	contextMenu->addAction(i18n("Copy Selection"), this, &XYFitCurveDock::resultCopySelection);
 	contextMenu->addAction(i18n("Copy All"), this, &XYFitCurveDock::resultCopyAll);
 	contextMenu->exec(uiGeneralTab.twGoodness->mapToGlobal(pos));
 }
 void XYFitCurveDock::resultLogContextMenuRequest(QPoint pos) {
 	auto* contextMenu = new QMenu;
 	contextMenu->addAction(i18n("Copy Selection"), this, &XYFitCurveDock::resultCopySelection);
 	contextMenu->addAction(i18n("Copy All"), this, &XYFitCurveDock::resultCopyAll);
 	contextMenu->exec(uiGeneralTab.twLog->mapToGlobal(pos));
 }
 
 /*!
  * show the result and details of the fit
  */
 void XYFitCurveDock::showFitResult() {
 	DEBUG("XYFitCurveDock::showFitResult()");
 
 	//clear the previous result
 	uiGeneralTab.twParameters->setRowCount(0);
 	for (int row = 0; row < uiGeneralTab.twGoodness->rowCount(); ++row)
 		uiGeneralTab.twGoodness->item(row, 2)->setText(QString());
 	for (int row = 0; row < uiGeneralTab.twLog->rowCount(); ++row)
 		uiGeneralTab.twLog->item(row, 1)->setText(QString());
 
 	const XYFitCurve::FitResult& fitResult = m_fitCurve->fitResult();
 
 	if (!fitResult.available) {
 		DEBUG("fit result not available");
 		return;
 	}
 
 	// Log
 	uiGeneralTab.twLog->item(0, 1)->setText(fitResult.status);
 
 	if (!fitResult.valid) {
 		DEBUG("fit result not valid");
 		return;
 	}
 
 	uiGeneralTab.twLog->item(1, 1)->setText(QString::number(fitResult.iterations));
 	uiGeneralTab.twLog->item(2, 1)->setText(QString::number(m_fitData.eps));
 	if (fitResult.elapsedTime > 1000)
 		uiGeneralTab.twLog->item(3, 1)->setText(QString::number(fitResult.elapsedTime/1000) + " s");
 	else
 		uiGeneralTab.twLog->item(3, 1)->setText(QString::number(fitResult.elapsedTime) + " ms");
 
 	uiGeneralTab.twLog->item(4, 1)->setText(QString::number(fitResult.dof));
 	uiGeneralTab.twLog->item(5, 1)->setText(QString::number(fitResult.paramValues.size()));
 	uiGeneralTab.twLog->item(6, 1)->setText(QString::number(m_fitData.fitRange.first()) + " .. " + QString::number(m_fitData.fitRange.last()) );
 
 	// show all iterations
 	QString str;
 	for (const auto &s : m_fitData.paramNamesUtf8)
 		str += s + '\t';
 	str += UTF8_QSTRING("χ²");
 
 	const QStringList iterations = fitResult.solverOutput.split(';');
 	for (const auto &s : iterations)
 		if (!s.isEmpty())
 			str += '\n' + s;
 	uiGeneralTab.twLog->item(7, 1)->setText(str);
 	uiGeneralTab.twLog->resizeRowsToContents();
 
 	// Parameters
 	const int np = m_fitData.paramNames.size();
 	uiGeneralTab.twParameters->setRowCount(np);
 	QStringList headerLabels;
 	headerLabels << i18n("Name") << i18n("Value") << i18n("Error") << i18n("Error, %") << i18n("t statistic") << QLatin1String("P > |t|") << i18n("Conf. Interval");
 	uiGeneralTab.twParameters->setHorizontalHeaderLabels(headerLabels);
 
 	for (int i = 0; i < np; i++) {
 		const double paramValue = fitResult.paramValues.at(i);
 		const double errorValue = fitResult.errorValues.at(i);
 
 		auto* item = new QTableWidgetItem(m_fitData.paramNamesUtf8.at(i));
 		item->setBackground(QApplication::palette().color(QPalette::Window));
 		uiGeneralTab.twParameters->setItem(i, 0, item);
 		item = new QTableWidgetItem(QString::number(paramValue));
 		uiGeneralTab.twParameters->setItem(i, 1, item);
 
 		if (!m_fitData.paramFixed.at(i)) {
 			if (!std::isnan(errorValue)) {
 				item = new QTableWidgetItem(QString::number(errorValue, 'g', 6));
 				uiGeneralTab.twParameters->setItem(i, 2, item);
 				item = new QTableWidgetItem(QString::number(100.*errorValue/std::abs(paramValue), 'g', 3));
 				uiGeneralTab.twParameters->setItem(i, 3, item);
 			} else {
 				item = new QTableWidgetItem(UTF8_QSTRING("∞"));
 				uiGeneralTab.twParameters->setItem(i, 2, item);
 				item = new QTableWidgetItem(UTF8_QSTRING("∞"));
 				uiGeneralTab.twParameters->setItem(i, 3, item);
 			}
 
 			// t values
 			QString tdistValueString;
 			if (fitResult.tdist_tValues.at(i) < std::numeric_limits<double>::max())
 				tdistValueString = QString::number(fitResult.tdist_tValues.at(i), 'g', 3);
 			else
 				tdistValueString = UTF8_QSTRING("∞");
 			item = new QTableWidgetItem(tdistValueString);
 			uiGeneralTab.twParameters->setItem(i, 4, item);
 
 			// p values
 			const double p = fitResult.tdist_pValues.at(i);
 			item = new QTableWidgetItem(QString::number(p, 'g', 3));
 			// color p values depending on value
 			if (p > 0.05)
 				item->setForeground(QBrush(QApplication::palette().color(QPalette::LinkVisited)));
 			else if (p > 0.01)
 				item->setForeground(QBrush(Qt::darkGreen));
 			else if (p > 0.001)
 				item->setForeground(QBrush(Qt::darkCyan));
 			else if (p > 0.0001)
 				item->setForeground(QBrush(QApplication::palette().color(QPalette::Link)));
 			else
 				item->setForeground(QBrush(QApplication::palette().color(QPalette::Highlight)));
 			uiGeneralTab.twParameters->setItem(i, 5, item);
 
 			// Conf. interval
 			if (!std::isnan(errorValue)) {
 				const double margin = fitResult.tdist_marginValues.at(i);
 				if (fitResult.tdist_tValues.at(i) < 1.e6)
 					item = new QTableWidgetItem(QString::number(paramValue - margin) + QLatin1String(" .. ") + QString::number(paramValue + margin));
 				else
 					item = new QTableWidgetItem(i18n("too small"));
 				uiGeneralTab.twParameters->setItem(i, 6, item);
 			}
 		}
 	}
 
 	// Goodness of fit
 	uiGeneralTab.twGoodness->horizontalHeader()->setSectionResizeMode(QHeaderView::Stretch);
 	uiGeneralTab.twGoodness->item(0, 2)->setText(QString::number(fitResult.sse));
 
 	if (fitResult.dof != 0) {
 		uiGeneralTab.twGoodness->item(1, 2)->setText(QString::number(fitResult.rms));
 		uiGeneralTab.twGoodness->item(2, 2)->setText(QString::number(fitResult.rsd));
 
 		uiGeneralTab.twGoodness->item(3, 2)->setText(QString::number(fitResult.rsquare, 'g', 15));
 		uiGeneralTab.twGoodness->item(4, 2)->setText(QString::number(fitResult.rsquareAdj, 'g', 15));
 
 		// chi^2 and F test p-values
 		uiGeneralTab.twGoodness->item(5, 2)->setText(QString::number(fitResult.chisq_p, 'g', 3));
 		uiGeneralTab.twGoodness->item(6, 2)->setText(QString::number(fitResult.fdist_F, 'g', 3));
 		uiGeneralTab.twGoodness->item(7, 2)->setText(QString::number(fitResult.fdist_p, 'g', 3));
 		uiGeneralTab.twGoodness->item(9, 2)->setText(QString::number(fitResult.aic, 'g', 3));
 		uiGeneralTab.twGoodness->item(10, 2)->setText(QString::number(fitResult.bic, 'g', 3));
 	}
 
 	uiGeneralTab.twGoodness->item(8, 2)->setText(QString::number(fitResult.mae));
 
 	//resize the table headers to fit the new content
 	uiGeneralTab.twLog->resizeColumnsToContents();
 	uiGeneralTab.twParameters->resizeColumnsToContents();
 	//twGoodness doesn't have any header -> resize sections
 	uiGeneralTab.twGoodness->resizeColumnToContents(0);
 	uiGeneralTab.twGoodness->resizeColumnToContents(1);
 	uiGeneralTab.twGoodness->resizeColumnToContents(2);
 
 	//enable the "recalculate"-button if the source data was changed since the last fit
 	uiGeneralTab.pbRecalculate->setEnabled(m_fitCurve->isSourceDataChangedSinceLastRecalc());
 }
 
 //*************************************************************
 //*********** SLOTs for changes triggered in XYCurve **********
 //*************************************************************
 //General-Tab
 void XYFitCurveDock::curveDescriptionChanged(const AbstractAspect* aspect) {
 	if (m_curve != aspect)
 		return;
 
 	m_initializing = true;
 	if (aspect->name() != uiGeneralTab.leName->text())
 		uiGeneralTab.leName->setText(aspect->name());
 	else if (aspect->comment() != uiGeneralTab.leComment->text())
 		uiGeneralTab.leComment->setText(aspect->comment());
 	m_initializing = false;
 }
 
 void XYFitCurveDock::curveDataSourceTypeChanged(XYAnalysisCurve::DataSourceType type) {
 	m_initializing = true;
 	uiGeneralTab.cbDataSourceType->setCurrentIndex(type);
 	m_initializing = false;
 }
 
 void XYFitCurveDock::curveDataSourceCurveChanged(const XYCurve* curve) {
 	m_initializing = true;
 	XYCurveDock::setModelIndexFromAspect(cbDataSourceCurve, curve);
 	m_initializing = false;
 }
 
 void XYFitCurveDock::curveXDataColumnChanged(const AbstractColumn* column) {
 	m_initializing = true;
 	XYCurveDock::setModelIndexFromAspect(cbXDataColumn, column);
 	m_initializing = false;
 }
 
 void XYFitCurveDock::curveYDataColumnChanged(const AbstractColumn* column) {
 	m_initializing = true;
 	XYCurveDock::setModelIndexFromAspect(cbYDataColumn, column);
 	m_initializing = false;
 }
 
 void XYFitCurveDock::curveXErrorColumnChanged(const AbstractColumn* column) {
 	m_initializing = true;
 	XYCurveDock::setModelIndexFromAspect(cbXErrorColumn, column);
 	m_initializing = false;
 }
 
 void XYFitCurveDock::curveYErrorColumnChanged(const AbstractColumn* column) {
 	m_initializing = true;
 	XYCurveDock::setModelIndexFromAspect(cbYErrorColumn, column);
 	m_initializing = false;
 }
 
 /*!
  * called when fit data of fit curve changes
  */
 void XYFitCurveDock::curveFitDataChanged(const XYFitCurve::FitData& fitData) {
 	DEBUG("XYFitCurveDock::curveFitDataChanged()");
 	m_initializing = true;
 	m_fitData = fitData;
 
 	if (m_fitData.modelCategory != nsl_fit_model_custom)
 		uiGeneralTab.cbModel->setCurrentIndex(m_fitData.modelType);
 
 	uiGeneralTab.sbDegree->setValue(m_fitData.degree);
 	m_initializing = false;
 }
 
 void XYFitCurveDock::dataChanged() {
 	this->enableRecalculate();
 }