Correction of Barometer Reading for Temperature
Because of the difference in expansion of the mercury column of a mercurial barometer and that of the brass scale by which the height is measured, a correction should be applied to the reading when the temperature differs from the standard used for calibration of the instrument.
To find the correction, enter the temperature in degrees Fahrenheit and the barometer reading. Apply the correction in accordance with the sign given. This correction does not apply to aneroid barometers.
The standard temperature used for calibration is 32° F for the mercury, and 62° F for the brass.