Ball Tetrahedron for intercomparisons with covers of the balls. These covers force the participant to use offset styli ... which makes the test "more interesting" (it´s harder to achieve small errors)
Cylinder square as it is made available for a just initiated inter-laboratory comparison.
Please note that cylinder squares allow for a large number of measurands to be verified, as squareness, parallelity, roundness, length, diameter, cylindricity, straightness, coaxiality, flatness, run out. All this with a very small uncertainty as such cylinders can be made very precise.
The problem is that these cylinders must be calibrated somewhere with high accuracy ... and of course the capability of the (accredited) calibration laboratories for cylinders and any other precise master parts must be assessed. This is what the inter-laboratory comparison is about.
We believe there is nothing better for proficiency testing of laboratories doing 3D calibrations and verifications when form errors and are involved. The tetrahedron (left side) allows for extremely quick machine stability checking ... however the validation of a lrger number of "real" measurement features other than mere distances can be done with this cylinder square.