how to change the units

Hello,

In Frame Maker I have opened 4 FM files at one time.

I have noticed that the units are all in "inches", but I would like to have the units in mm.

So in the first FM opened document, I gone in View/Options and change it from inches to mm and it worked.

But for the others documents they remain in "inches".

How to set the unit in mm in the preferences ? Or is it a way to have the units in mm for all documents I will open ?