This is a simple model for calibrating filament shrinkage in the Z axis. The original CAD file was generated by Claude and subsequently modified by me. 

In the simplest case, use calipers to measure from the top of the tall block to the top surface of the base. It should be 50mm. Do not measure to the surface the model is sitting on, it will not be as accurate.

You can also measure similarly but using the smaller block, which should be 10mm, which will give you some idea of relative shrinkage at small & large scales. I have not used this aspect yet.

The notches are there to help keep the calipers straight, if that seems useful.

For XY shrinkage, I've been using this: