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How to Set a Precision Instrument Barometer

A barometer measures changes in atmospheric pressure. Differences in atmospheric pressure indicate an approaching change in the weather. Generally, if the pressure drops a storm is on the way, and when the pressure rises the weather is improving. Precision Instruments manufactures aneroid barometers which have a metal capsule that changes in size with atmospheric pressure changes. The changes in the metal are then transferred to the needle of the barometer that points to the pressure on the face of the barometer. For accurate readings, your barometer must be set properly.

Things You'll Need

Computer with Internet
Barometer
Small jeweler's screwdriver

Instructions

- 1
  Access the most current barometric reading for your location. The most current readings will be available on the Internet from reliable sources such as the National Oceanic and Atmospheric Administration (NOAA).
- 2
  Subtract 7.5 mmHg (millimeters of mercury) from the atmospheric pressure in Step One for every 100 meters you are located above the weather station. If your elevation is lower than the weather station, subtract 7.5 mmHg from the pressure reading for every 100 meters. This step is optional but will give you more precise results for your location.
- 3
  Locate the small hole in the back of your barometer. Insert the screwdriver into this hole. Watch the face of the barometer as you turn the screw whichever direction moves the hand of the barometer clockwise.
- 4
  Continue turning the screw until the indicator lines up with the current atmospheric pressure you obtained in Step One or Step Two.
- 5
  Turn the dial on the face of the barometer. This moves the larger hand that indicates the current weather conditions such as fair, stormy or calm. Turn it until the hand lines up with the current weather. Not all Precision Instruments barometers have this.

Nature