A test for benchmarking the printbed adhesion. The bottom surface has irregular surface with wholes to make it more difficult to print the bottom layer.
There are also bridges and diagonals for benchmarking the printers abilities.
The printbed adhesion can be measured by pulling with a springscale at the towers top.

This was part of a research project at the University of Stuttgart:
http://dx.doi.org/10.18419/opus-3398