Using a wind indicator as a rangefinder.
Anyone notice at the start, the sniper told the girl to Range Me and she picks up a wind speed indicator and uses that to give him the distance and direction?
shareNo, just mediocre editing. Shown especially after that, "range me" results in her looking through a spotting scope and using the rangefinder grid in there.
So, she just read out what she'd either just read from the scope, or had written on a range card we cannot see, and is getting the current wind wx data at the last moment.
Not that they did anything else right (ghillie suits and no other concealed position? Flinch at every shot...) nor was is a very good movie in any way. Lots of other mistakes.