This simple tool can asist in measuring the amount of z axis tilt away from perpendicular with respect to the x & y axes of a cnc router. It has a 1/4" (6.35mm) shaft which can be insesrted into the collet of the router. Then just slowly lower the z axis to see if all four contact points touch the bed at the same time. If not it will indicate the tilt direction.

I printed this with supports, and I also printed it with 100% infill to make it a bit more rigid and robust.