Does the instrument for B.P. have to be calibrated each time you travel to a new location? I know it does, but should the new calibrated pressure be used, or the uncalibrated?

Any measuring instrument must be periodically calibrated to insure that it is in tune with reality. I have used several different instruments for measuring barometric pressure. These include the Casio Triple Sensor watch to expensive digital instruments used by surveyors to determine the barometric pressure.

So far, I have had little detectable error in moving from one geographical location to another. As I mentioned above, when the opportunity presents itself, or the information is available, you should update your pressure sensor.

One of the easiest ways to do this is to call the airport nearest your location. The closer you are to the airport, the more precise your calibration will be. Call the weather office for the airport and ask for the UNCORRECTED AIR PRESSURE. This is different from the Corrected air pressure. Re-calibrate your pressure sensor to the new data provided.

Under the best conditions, you would do this while standing at the airport. This way there is little or no chance of the pressure gradient being different between the airport and your real location. Distance in miles, altitude differences and other weather conditions would cause a deviation between the data provided by the airport and your own sensor.

If I read correctly, the uncorrected pressure is the pressure to use for the math sequences. Am I correct here?

Glad to see you on the board!

Yes the Uncorrected Air Pressure is the data that you want to be using. This gives the shooter the actual measured barometric pressure as taken at the station reporting the data.

For the unfortunate shooter that has NO reference to barometric pressure, there are tables of standard air pressures for listed altitudes above sea level. There is error in this also.

For example, where I live in Minnesota, the altitude above sea level is around 350'. The average air pressure should be something less than 29.53 (SAC). The 8 month running average that I have determined is a little higher than 29.90. WHat's up with that?

Good to be back, thanks.