Comment # 27 on bug 1124508 from Felix Miata

(In reply to Stefan Hundhammer from comment #25)
> Felix, you are definitely right that screen resolution does make a difference,

That's incomplete, thus inaccurate. Standing alone, screen resolution makes no
difference. It's the combination of screen resolution and screen size that make
a difference. The two combined are called display density, measured in DPI or
PPI, commonly labeled HiDPI when the display's actual physical number is some
arbitrarily above average number, likely the angularly defined reference pixel
density 96 from CSS specifications times two, 192.

192 is reached on 4K screens at just under 23". On 2560x1440 192 is at just
under 15.3", and 1920x1080 just under 11.5".

Note in my comment #13 screenshot the reported 120 DPI is a logical DPI
resulting from software settings. Logical DPI is the "knob" used for GTK/Gnome
"scaling". Under the covers that knob is xrdb's Xft.dpi, which QT/KDE respond
to when present, and indeed is implementor of the KDE desktop settings font tab
value for "DPI". Physical PPI is the important number determining usability,
the actual physical pixel density.

> but please don't forget that this is the inst-sys with a much
> more restricted environment and no KDE/GNOME/Xfce/whatever desktop to get
> any defaults from.

I get that. I think QT has a built-in initial value of 9pt, maybe 10pt, based
on what I remember appears in the fonts tab when qt5ct is initialized on a
virgin installation.