The Part drawings and the Measure tool were all in inches. The Drawings were defaulting to metric. Yes – I was using the menu opened by “File”.
I had to edit the Part quite heavily when I corrected what had originally been my mistake reading the original drawing, because moving the hole also altered the outline (optionally perhaps, but it seemed better to do that at the same time).
Only, I had to do this twice because I mis-read or miscalculated the change.
I knew editing the Part would edit the assembly as well but it didn’t appear to change the drawing and I didn’t know about the “Re-project” move. At this stage the drawing’s purpose was for ensuring I had placed the holes in the brackets correctly. I can add the other dimensions later.