A barometer measures air pressure. Some barometers measure air pressure in inches of mercury, but others may measure in torrs, or milligrams of mercury. You can convert the air pressure from torrs to inches using a simple mathematical formula. Some barometers may also measure air pressure in millibars; you can convert millibars to inches using multiplication.
Things You'll Need
Verify the barometer's accuracy. Listen to a weather report or look up the current air pressure online. If the barometer needs adjusting, find the adjusting screw on the back of the barometer. Turn the screw until the needle points to the current air pressure.
Read your barometer. Note whether it measures in inches. If so, it will tell you the air pressure measured in inches of mercury.
Convert measurements for readings that aren't in inches. If your barometer measures millimeters of mercury, convert to inches by multiplying the reading by 0.03937. If your barometer measures air pressure in millibars, convert to inches by multiplying the reading by 0.02953.
- Photo Credit barometer image by Peter Baxter from Fotolia.com
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