This is a model that I designed to check how level my bed was.
The model should be 0.8mm thick at all points.
It is designed so that it is easy to use a calipers to measure the height of all the points on the model.
This test can also be used to check if your print surface is warped and to find where your printer thinks the center point of the bed is.

More information about the design and use of this print can be found at: conor.engineer/2018/06/16/3d-printer-bed-leveling-warping-test