Calibration cube

I used this model to check the calibration of my 3D printer.

It should come out as a cube if X- Y- and Z- axis steppers are moving in the correct relative step size.
The walls should be straight, and have unform thickness.

The circle cutouts make sure that the relative spacing of Z-axis steps with the other axis is correct. Mis-configured Z steps will result in an oval. The circle also (crudely) estimates the overhang angle for this material at the top, where the edge is nearly tangent to the printing plane.