Shooter's MOA

Shooter’s MOA, sometimes written as IPHY for inch per hundred yards, simplifies the minute of angle to a clean one inch at 100 yards instead of its real geometric value. The appeal is mental arithmetic, because a one inch increment scales neatly to two inches at 200 yards, three inches at 300 yards, and so on. Many shooters use this approximation in the field without ever noticing a problem inside normal ranges.

The catch is that the rounding compounds with distance, so the gap between this convention and true MOA grows the farther you shoot. At long range that drift can be enough to miss, since a turret built on one definition will not perfectly match a calculation built on the other. Knowing which standard your click value actually follows is part of understanding the broader MOA vs mil question.