Gravity Barometer Reading
Correction Calculator
This calculator requires the use of Javascript enabled and capable browsers. This script determines the error in an observed barometer reading, based on gravity differences in different latitudes. Because the Earth is not a perfect sphere, the acceleration due to gravity depends on latitude. The radius of the earth is greater at the equator than at the poles. This means that gravity is least at the equator and greatest at the poles. Thus at smaller latitudes the mercury in the barometer tube weighs less, and will require a greater length to balance a given pressure. The barometer is calibrated for a latitude of 45 degrees. For latitudes less than 45 degrees, the correction should be subtracted from the observed height; for latitudes greater than 45 degrees the correction should be added. The default values are typical for the general lower desert area of Southern California. To use the calculator, enter the latitude and the known and observed barometer reading in either designation, then click on Calculate. Results are yielded in both inches of mercury and millibars. If you don't know the latitude, you can use our USA longitude and latitude map to get an idea of the general area. There is also a latitude correction chart below the calculator. Other pressure correction calculators are for temperature correction only, for altitude correction only, for temperature and altitude correction and for gravity, altitude, and temperature correction.
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