I use an app called On Target, available for free. The app has a list of bullet diameters. Scan the target, choose the diameter bullet, center the target circle (circle of bullet diameter size) on each bullet hole and read the size of the group on the Rt side in inches or MOA. Works very easily. It's possible to even keep a record of all scanned targets. It also computes distance to center of group and other vital stats. You can also input the POA and it will compute the vertical and horizontal distance of the group center from the POA.
I acquired it for free a couple of years ago, but haven't checked recently for availability, upgrades or cost.
