We are looking for the average humidity in the location where you will be hunting or shooting as a percentage. Your turret will remain accurate 20% above and below the entered value (i.e. you have a 40% window to work with). The average humidity for most of North America is 78%. However, the easiest way to find the average humidity in your location is a simple google search (e.g. average humidity 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.