How to Calibrate a Weather Station Barometer

Aneroid barometer

A barometer is an instrument that measures the pressure of the atmosphere at a given location. The most common type of barometer is the aneroid barometer. Aneroid barometers employ a sealed, thin-walled metal cell. Changes in the atmospheric pressure cause the container to expand and contract which moves a needle attached to the cell to indicate the air pressure. Air pressure is measured in inches of mercury or in millibars. The average air pressure at sea level is 29.92 inches of mercury, which is equal to 1013.25 millibars. Aneroid barometers are calibrated by turning an adjustment screw on the back of the case.

Things You'll Need

• Aneroid barometer
• Small screwdriver
• Computer with Internet connection

Instructions

1. Navigate to aviationweather.gov. Find "Local forecast by city, state or zip code." Enter appropriate information. Read barometric pressure under "Current conditions."

2. Get local (within 100 miles) barometer reading from local TV news stations (or their websites).

3. Dial 1-800-wxbrief and follow the voice instructions. The altimeter reading reported for a city near you is the barometer setting. For example, "altimeter 29.98" is the barometric pressure in inches of mercury.

4. Turn the screw on the back of the barometer with the small screwdriver to adjust the aneroid barometer to the correct barometric pressure.

Tips & Warnings

• It is not important to know the exact barometric pressure to forecast the weather. What is important is whether the barometric pressure is rising or falling. A rising barometer usually means fair weather, while a falling barometer usually indicates windy or stormy weather.

• Barometers are very delicate instruments and are easily damaged by rough treatment.

References

• Nasa: Air Pressure
• Aviation Weather: Barometric Pressure

Resources

• The Weather Prediction: Forecasting Tools