What Is CEP (Circular Error Probable)?
What it is
CEP (circular error probable) is the radius of a circle, centered on your group, that contains at least 50% of your shots. It's a borrowed military/ballistics term, but the idea is simple: instead of an average that a single flier can skew, CEP tells you the radius your "typical" shot lands within — the flier just ends up outside the circle instead of dragging the whole number up.
How we calculate it
We measure every shot's distance from the group's center, sort those distances, and take the median — the distance where half the shots are closer and half are farther. That median distance is the CEP radius.
Why it matters
A single wild flier can make a group's average spread look much worse than the group actually shoots most of the time. CEP is more resistant to that outlier, so it's a steadier number to track session over session — it answers "where do most of my shots actually go," not "what's the worst-case spread this session."
See this measured on your own groups
Range Tracer calculates what is cep? automatically for every session you log.