Holey calibration just makes holes or ¼ inch deep pokes. The first time I tried the Holey Calibration the Z feed bottomed skipping teeth on the belt in both directions, but it made holes. I e-mailed the factory to find out what I was doing wrong to have my Z axis driving so far and I got suggested settings for the Z axis setup in GroundControl that worked much better. Specifically they suggested a pitch of 18 and an encoder setting of 5400, I don’t understand why as I don’t understand what GroundControl is doing with those numbers. I had used actual measured pitch or how much the router moves for one rev of the lead screw but the encoder number isn’t easily discerned so I accept the magic as it appears to work.
I don’t remember my encoder setting though it should be the default and my pitch is 26 on my Metal Maslow. I can’t vouch for mm accuracy because my material isn’t necessarily totally flat. My cuts are coming out +/-1mm even with the uneven surface.