This is a kit for leveling the bed of Prusa MK2/MK3 and similar when the bed warp is too severe for the automatic calibration to handle it properly.
The included tweezers is an absolute time saver, in fact I found it next to impossible to squeeze the stack of washers+spacer under the MK3 bed which is full of magnets.
How to use: you add a couple M3 spring washers under the bed spacers (more where needed but keep in mind each washer is 0.5-0.8mm). You then measure and adjust as needed until the mechanical warp reduces.
In my case I got a 10x reduction in warp (from 600 microns to about 50 - couldn't get further because the remaining warp is between the screws and is S-shaped).
The repeatability of the dial mount seems to be around 20 microns (0.001") when moving along X axis and 3 microns when moving Y axis (0.0001"), note that the copper traces and the white paint also have thickness that influences the reading.
The dial indicator mounts to the printed part using an M6 20mm screw (or a 1/4"-20 3/4"). The printed part clips on 8mm rods, 45mm apart - which is typical for Prusa MK2, MK3, etc.
My Prusa MK3 had a +460/-600 micron variation across the bed and the automatic calibration couldn't handle that, so I was confined to printing on a portion of the bed. I learned about the spring washer trick so I set to do that over the weekend but I found some challenges:
1st - the dial mount indicators on thingiverse didn't quite work for me (either not repeatable enough or too involved to move around the print head) or simply didn't work with my dial (which are set to horizontal mount) so I designed a new fully printable quick-release indicator that leverages my Rod Clasp design (https://www.thingiverse.com/thing:2932583) and can takes both horizontal and vertical dials.It's a breeze to detach and move to the other side of the print head to measure the extreme edges of the bed).
2nd - I found that mounting a stack of washers under a magnetic bed is a sisyphean task so I designed a special set of tweezers.