When I open new diagram in Dia Diagram Editor (version 0.97+git, compiled Feb 14 2020), default zoom is 100%.
But it shows 96 cm on full width ruler of my notebook screen, which is exactly 34.4 cm wide.
So, it shows alleged 100% zoom as real 35.8% zoom.
I use Xfce 4.16 on Debian GNU/Linux 11 with custom 142 DPI in appearance setting (screen has width 1920 pixels).
My X.Org X Server 1.20.11 correctly detects size of screen in millimetres and pixels, but it sets DPI to 96 for me for unknown reason (as I can read in my /var/log/Xorg.0.log).
Even if Dia would read this Xorg DPI resolution, 35.8 % ratio cannot be calculated in my opinion (96DPI / 142DPI = 67.6%)
(Another applications like Libre Office Draw show paper size A4 width in 100% zoom as real 21 cm.)
Please, what can be wrong?