If it’s out it’s only by a touch, which could be because I’m eyeing things up.
I click on the left mounting hole, unlock, and change x coordinate to 1.0. It locks on 1.001" - It tends to snap to certain numbers -
I click on right mounting hole. unlock, and change x coordinate to 3.952. - 75mm divided by 25.4 plus 1 - It locks on 3.952"
I zoom in to max zoom, to get more accuracy, and put the mouse pointer on the left edge of the left hole copper and get 1.306".
I now do the left edge of the right hole copper and get 4.258"
4.258 - 1.306 = 2.952"
2.952 x 25.4 = 74.98mm
It’s a touch out, but one hole did lock on 1.001".
It’s pretty much std practice to go from edge to edge of same sized hole because you can’t get accuracy guessing the centres.
I know there is a bug when locating PCB, like you enter 2.0 and it changes to 2.001, but it wasn’t that important for me to have it that accurate.