Issue practically solved - workaround found
First: Thanks to all those that invested time to help me solve my problem! I appreciate that a lot.
Here the outcome: The issue is apparently not caused within Sketchup itself.
Let me explain what I found:
The Sketchup installation that caused my problems is running on Win 7 Professional. The system is running as a virtualized machine within VirtualBox.
I usually access the virtualized system from a rather outdated Notebook (therefore running Xubuntu) using Linux´ ‘rdesktop’ command. I have not experienced any issues with this setting so far, so I was not in doubt that the display as such was correct and the issue with the odd display of measurements was caused by Sketchup.
Accessing the very same virtualized System from another Win 7 Professional (‘real PC’, not virtualized) gave me measurements that displayed exactly as expected.
I am not expert enough to finally judge on this, but it appears that the ‘rdesktop’ implementation within Linux behaves different from Window’s native ‘mstsc’ program for accessing remote displays.
Thanks to all involved and have a nice new year!
Keywords: Sketchup, Linux, Xubuntu, rdesktop, rdp, mstsc, display, dimensions