unit of measurement

I have set my preferred unit of measurement to “points” in General Preferences.
But when I change object positions (for example rehearsal marks) in Engrave Mode, positions are still showing as inches with fractions (which is really inconvenient). Is there a different unit setting somewhere?

No, all of those kinds of offsets in the Properties panel will always be measured in fractions of spaces. We have no current plans to change this.

Out of curiosity: In the German version this is metric? I am German and have been struggling with imperial units for 30 years.

They’re not metric or imperial. They’re just spaces. A space is the gap between two staff lines (of a five line staff).

The advantage to measurements being in spaces is that if you change staff size, everything attached to the stave adjusts accordingly.

And to complete the circle: the staff size (which is 4 spaces if I’m not mistaken) is expressed in metric units (millimetres) in the Page Layout section.
So you could calculate spaces to millimetres (and to points) if you really wanted to.

Here is a chart that equates rastral sizes to mm. The measurement is from bottom line to top line of a five-line staff.