How Can I Test a Dial Barometer?

The dial barometer

Calibrating your barometer is the first step to making local weather predictions. Barometers measure atmospheric pressure and so are sensitive to changes in pressure that accompany storms (low pressure), return to fair weather (high pressure) or changes in altitude. The dial barometer is the easiest to calibrate. A few simple steps will align the readings on your barometer with readings from a local weather station.

Things You'll Need

• Dial (aneroid) barometer
• Small flat head screwdriver
• Calculator

Instructions

1. Obtain a precise measurement of altitude (in feet) for your home address by visiting the website Veloroutes. Type in your street address and zip code and then click "Find elevation."

2. Find weather stations near your home on the Weather Underground website. Enter your zip code and click "Go." This site automatically selects a nearby weather station.

3. Correct for differences in altitude using this rule of thumb: Pressure decreases 0.01 inch for each 10 feet of elevation gain. Example: If your house is 50 feet higher in elevation than the weather station, subtract 0.05 inch from the pressure reading reported by the weather station. If the weather station pressure equals 29.97 inches, the pressure at your home equals 29.97 minus 0.05 or 29.92 inches.

4. Adjust the needle on your dial barometer to the altitude-corrected reading from the weather station. Turn the calibration screw on the back of the barometer so the needle lines up with the adjusted reading. Tap the barometer gently and readjust the needle if necessary.

5. Recheck the pressure reading from the weather station the next day, and then repeat Steps 3 (altitude correction) and 4 (needle position adjustment).

Tips & Warnings

• Small pressure differences between a nearby weather station and your barometer do not affect its usefulness for monitoring weather.

• Barometric pressure readings alone do not predict weather. Wind strength and direction, cloud patterns and temperature readings are also important.

• A dial barometer and an aneroid barometer are the same thing. "Aneroid" means "without fluid." Aneroid barometers sense pressure changes with a thin-walled metal cylinder that flexes as pressure changes.

References

• Home Weather Stations Guide: The Aneroid Barometer Is the Choice of Today's Weather Watchers
• Australian Government Bureau of Meteorology: The Aneroid Barometer and How to Use It
• USA Today: Understanding Air Pressure
• Veloroutes: Elevation Map, Latitude/Longitude of Your City or Address
• Weather Underground