How to Adjust the Barometer to Read the Sea-Level Pressure

A barometer is a device that measures atmospheric air pressure using a column of mercury (mercury barometers) or a flexible metal cell (aneroid barometers). Changes in atmospheric air pressure are used to determine weather changes; rising pressure generally signals fair weather and falling pressure signals stormier weather. While air pressure varies depending on altitude, the change in local air pressure is what matters in terms of weather prediction; it is not necessary to synchronize your barometer to sea level air pressure to predict the weather. However, since weather forecasters deal in sea level measurements, adjusting your barometer can simplify its use.

Things You'll Need

• Small screwdriver (for aneroid barometers)

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Instructions

1. • 1

     Determine the air pressure at sea level by watching a local weather forecast; weather stations have already calculated local air pressure to sea level.

   • 2

     Use a small screwdriver to adjust the screw in the back of an aneroid barometer. Adjust the reading to match the local sea level air pressure.

   • 3

     Raise or lower the mercury reservoir in a mercury barometer until the top of the mercury column matches the local sea level air pressure.

   • 4

     Re-adjust the barometer periodically to match local sea level air pressure, particularly for aneroid barometers, as the flexible cell used to measure air pressure can loosen over time.