I was looking for a calibration object I saw some time ago that looked a lot like this, with the X and Y axis marked on it. Since I couldn't find it, I decided to throw one together. Maybe someone else will be able to use this too.
The long sides are 40mm long. All the other shorter sides are 20mm.
Update: I was having issues with the model that has the cutouts so I uploaded a version with raised letters. For some reason, the slicer was really messing things up.