What causes a parallax shift? Is it temperature or barometric pressure? I’m shot 2 days ago it was 55F and 30.19”. I shot again yesterday at 68F and 29.93”. The parallax settings were different at each yardage marker (did the whole head nodding without touching the rifle until the reticle didn’t move at least vertically can never get the horizontal movement out of my NightForce 5-25 ATACR but I guess that’s be a different topic). Anyways the setting were different by a fair amount on the two days so I’m just wondering what is the cause of that?