circular error probable

CEP concept and hit probability. 0.2% outside the outmost circle.

Circular error probable (CEP), also circular error probability or circle of equal probability, is a measure of a weapon system's precision in the military science of ballistics. It is defined as the radius of a circle, centered on the aimpoint, that is expected to enclose the landing points of 50% of the rounds; said otherwise, it is the median error radius, which is a 50% confidence interval. That is, if a given munitions design has a CEP of 10 m, when 100 munitions are targeted at the same point, an average of 50 will fall within a circle with a radius of 10 m about that point.