We are looking for the average barometric pressure in the location you will be hunting/shooting, measured in inches of mercury (inHG). The average barometric pressure for most of North America is 29.53 inHG. However, the easiest way to find the barometric pressure in your location is a simple google search (e.g. barometric pressure in 'my location'). In general, barometric pressure and humidity have a fairly small impact on your turret's overall accuracy, but the more accurate the values you provide are, the more accurate your turret will be.