Quote Originally Posted by Carlb1058 View Post
1) measure the distance between the axis and a convenient point
Measure how far the axis moves. So for example on X move the gantry to one end, then turn 20 turns (or whatever) and measure how far it moved. You don't need access to the screw.

The meter you have will be fine. Just connect the negative probe to negative, (i.e. ground) and the other one to the correct pins. You may have to unscrew the board to access one of them.