GNOME calculator: https://upload.wikimedia.org/wikipedia/commons/4/40/GNOME_Calculator_3.14.90.png

Windows calc.exe: https://mspoweruser.com/wp-content/uploads/2019/03/Windows-calculator.jpg

OS X calculator: http://cdn.osxdaily.com/wp-content/uploads/2015/05/scientific-calculator-mac-610x353.jpg

All three label trig buttons in lower case. It seems evident KCalc should, too.

Could you investigate if it is possible to use log_10 instead of log, as is done in the OS X screenshot? Superscript seems possible, but I am not sure about subscript.

https://en.wikipedia.org/wiki/Unicode_subscripts_and_superscripts

Of course it's possible, by using <sub>:

Alternatively, we could simply substitute lg for log_10.

I would prefer showing the base instead of lg, but don't know if it would work with all font sizes. In the statistic and numeral system modes, the buttons all make sure the text has a maximum of 3 characters (e.g. Mea instead of Mean).

lg is, in fact, the ISO standard[1]. However, log_10 is the least ambigious. The length looks fine. We have a x*10^y after all.

[1] https://en.wikipedia.org/wiki/Logarithm#Particular_bases