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pressure (the pressure your location would be at if located at sea-level) is generally higher than your
measured pressure.
Thus, your absolute pressure (measured at your location) may read 28.62 inHg (969 mb) at an altitude
of 1000 feet (305 m), but the relative pressure (sea-level) is 30.00 inHg (1016 mb).
The standard sea-level pressure is 29.92 in Hg (1013 mb). This is the average sea-level pressure
around the world. Relative pressure measurements greater than 29.92 inHg (1013 mb) are
considered high pressure and relative pressure measurements less than 29.92 inHg are considered low
pressure.
To determine the relative pressure for your location, locate an official reporting station near you (the
internet is the best source for real time barometer conditions, such as Weather.com or
Wunderground.com), and set your weather station to match the official reporting station.
5.4
Barometer Calibration
Your barometer will operate from -100 to 3,000 feet with reliable accuracy. Aneroid barometers have a
small screw on the back for sea-level calibration. With a flat blade screwdriver, turn this screw in
either direction slightly while looking at the indicator needle. It should move in one direction or the
other. Tap the barometer to see where the needle settles. Continue this procedure until the proper
pressure reading is obtained. Do not turn the screw counter-clockwise (to the left) too far, since the
screw can fall out. After the initial calibration, no further adjustment will be required unless the
barometer is moved to a new geographic location.
Figure 1
Barometer Back Plate
