I recently upgraded my Wanhao Di3 to a RAMPS v1.4 running Repetier v0.92.9, partly as I wanted some extra functionality with the latest release and more control and also because I have had 2 Melzi boards fail on me now within 18 months!

The upgrade wasn't too hard but takes a bit of time getting everything calibrated and functioning correctly, one of the issues I found was tuning the steps per mm for the X, Y and Z axis (to a decent tolerance).

https://youtu.be/sEtmlaI2Q9c

This is where the Axis Caliper Alignment Jig came about, the video should explain everything and this should work on most metal framed Prusa variants, but I am sure this is easily remixed to accommodate most printer setups.

All parts are designed to be printed without support, see the orientation image for the main caliper block, the angled edges are all above 45 degs.

Couple of further notes:

1) I only show Repetier software here, it is also possible to enter Gcode directly to produce the same result.

2) The caliper used is just a cheap one from Aliexpress and is probably the most common form factor, so the jig should be widely useable. If it doesn't quite fit, my excuse is I didn't have a caliper to measure the caliper, but should be ok as I made 2 prior prototypes to tune it to a satisfactory level.