pattern wherein the reference element 18 arranged in the longitudinal line 20 and in the transverse line 22 may not be exactly positioned on these lines 20 and 22 but have a slight offset 0 from these lines as schematically indicated for the reference elements 18 u2033 in this way errors in the electronics and in the cnc control for example rounding errors summation errors and the like can be determined because other x and y values must be determined for their position in the illustrated exemplary embodiment the reference elements 18 are constructed identically however reference elements having different shapes and or different sizes can be attached on the support 10 each reference element 18 is configured as a sleeve and has an interior surface 24 in the form of a circular cylinder the outside is formed by an exterior surface segment 26 in form of a truncated cone and an exterior surface segment 28 in form of a circular cylinder the exterior surface segment 28 in form of a circular cylinder abuts the top side 12 of the support and the exterior surface segment 26 in form of a truncated cone tapers down with increasing distance from the top side 12 the reference elements 18 can be glued to.