Calibration tool with Z axis test

This calibration tool has a 20mm square base and has steps of 10mm intervals up to a height of 40mm.

This tool let's you test the accuracy of all three axis but unlike a simple 20mm cube if you have an issue with the Z axis you can test whether it is due to errors in the Z step value or whether it is a z offset issue. You can see in my case that I have a consist .3 reduction in height regardless of where measured so in this instance it is a z offset/start issue (probably).

If it's a z step issue the error will increase the higher up you take the measurement.

In my photos I'm using a cheap vernier from amazon approx $10 and only has a resolution down to 0.1 mm but for most things this is adequate