When it comes to UI for configuring the computer/workspace, there are controls which involve quantities with units/symbols. And some (physical) quantities could be noted with SI (International System of Units) symbols (e.g. "s" for seconds), but also with informal (e.g. "seconds" or "secs".) Where the first might appeal to technical people, but could be a challenge for less technical persons.

Currently there is no consistency in what kind of unit symbols are used. In the config UI of Plasma and its various (3rd-party) applets there are e.g. all of "s", "secs" and "seconds" used.

Next to that also sometimes there are issues with support for localization as well as mistakes in proper english notation (spacing between number and unit/symbol depends on unit/symbol).

So the HIG should have

• some rules which type of units (SI or informal) to use in which situations
• a list of common pitfalls as quick reminder for developers who (like me) might not remember the correct spacing in English e.g. between number and percent symbol or number and arcminute symbol
• best practice for unit supporting i18n code with spin boxes & similar quantity control/display UI elements

A related discussion about proper i18n notation of numbers with units in general started on the translators' mailinglist: "RFC: Notation of numbers with (physical) units/symbols"