Put it in if you like but it is for longer zeros as Andy said, where an atmospheric change could put your zero a couple inches high or low so the app can account for that.
I just put in a theoretic 900hpa 9degc 10% humidity vs 1200hpa 30degc 80% humidy and got 0.1 of an inch variation of result @ 200y so that is 0.05 of an inch(that is only 1.27mm or put another way even if you had 1/8th MOA clicks it is still less than half a click )variation at 100y zero range with a humongous atmospheric change so shes pretty safe to ignore it if zeroed at 200 or less.
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