Being a nationalist, and as the common measure standard in my country is based on the meter, I of course converted every inch-based value to millimeters and used it in my CAD-tool, which was Cadstar at that time. If I only knew better at that time...
That particular tool (as well as several others, I am sure!), internally converts the values given i millimeters to inch-based values (mils), and since this inevitably gives round-off errors I had a tremendous work in getting everything to look as I wanted.
My advise is that, even if you think and walk i millimeters, to use inch-based values (mils) whenever you are going to do any work in an EDA-CAD program, be it schematics or layouts (especially layouts!).
Also, circuit-board makers more likely than not have their drills in mils, not in millimeters. So even then, when you are sending them the drill-file for the circuit-board, they are rounding off the drill sizes to mils, and which can result in too small clearance sizes for the pads and numerous other unforeseen errors.
Pim