Used to calibrate dimensional accuracy:

Outer dimensions 25x25x5mmInner dimensions 20x20x5mm

If your printer is printing diffrent, you need to adjust

1. Initial layer horizontal expansion (elephant foot)
2. Hole horizontal expansion (if inner dimensions are correct) - Inner dimensions wrong will cause outer dimensions wrong.
3. Horizontal expansion

You may also scale up Z to 25x25x25 to test Z axis accuracy (mostly dependant on slicer settings, not Z steps per mm) see prusa steps calculator