Mean Radius
The average distance of every shot in a group from the group's center, a more stable accuracy metric than a two-shot extreme spread.
Mean radius is the average distance from each shot to the calculated center of the group, taking every hole into account rather than just the two that landed farthest apart. Because it uses the whole population of shots, it judges a tight cluster with one flyer far less harshly than a center-to-center extreme spread does, and it converges on a meaningful value with fewer rounds.
Statisticians and serious load testers favor mean radius precisely because it is more stable from one group to the next, much as a standard deviation describes velocity spread better than a single high and low pair. Most modern target apps compute it automatically, giving you a single number that fairly summarizes the dispersion of a load.