Measure center to center for group size. (not outside to outside).
If you look at the jaw position it looks like it is over 30mm, close to 32mm or 1.26, if you subtract .223 it's close to the displayed group on the readout. This is how I measure groups and is far easier than doing math, measure one bullet hole, re-zero caliper, measure group. This method automatically compensates for centre to centre.