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Why doesn‘t my barometer read the read the same as the weather forecast?

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  • Created Jan 16, 2003
  • Updated Jul 6, 2004
  • Article #1138

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If your Barometer readings do not agree with the local airport or television station, it is because you are looking at two different kinds of readings. “Station pressure” is the true pressure at your site, or station. This is the pressure a mercury barometer would read in your classroom. This is also the pressure that your Vernier Barometer is calibrated to read. “Sea-level pressure” is the pressure after the station pressure has been adjusted to its equivalent at sea level. Airports and television stations usually report the sea-level pressure rather than the station pressure. This is commonly done to take altitude out of the equation for weather forecasters. To determine your station pressure when only sea-level pressure is known, visit

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/barfor.html#c3

The Barometric Formula is explained along with boxes to input the information from your local television station or airport. Your true station pressure is reported in mm Hg, in Hg, and kPa.

Using the Barometer as a weather station
If you want your Vernier Barometer to read sea-level pressure instead of station pressure, you can adjust it one of two ways. You can either adjust the sensor itself or you can do a one-point calibration using Logger Pro 3 software.
1. There is an offset potentiometer that you can use to adjust the pressure reading up and down. There is a small hole on one end of the Barometer with a small slotted screw inside. A small jeweler’s screwdriver can be used to turn this screw. This is a 15-turn potentiometer, so the adjustment can be made very gradually. Simply monitor the readings from the Barometer and adjust the screw until the readings match the airport or television station readings.

2. To perform a one-point calibration in Logger Pro 3 (version 3.3 or newer), plug in the Barometer and start Logger Pro. Choose Calibrate from the Experiment menu. Make sure the check box next to one-point calibration is checked and click on Calibrate Now. Enter the corrected value for your station pressure. Click Keep and then Done. Make sure the units for the value you enter match the units in the calibration.

* Note that you will need a mercury barometer if you ever wish to change the calibration back
to the station pressure.

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