BAROMETER ERRORS
Any inaccuracy of the instrument can be determined by comparison with a precision instrument, the National Weather Service provides a comparison service. The shipboard barometer should be corrected for height, before comparison If there is reason to believe that the barometer is in error, you should be compare it to a standard, and if an error is found, the barometer should be adjusted to the correct reading, or a correction applied to all your readings.
HEIGHT ERROR
The atmospheric pressure reading at the height of the barometer is called the station pressure and is subject to a height correction in order to make it a sea level pressure reading. Isobars reflect wind conditions of pressure only when they are drawn for pressure at constant height or the varying height at which a constant pressure exists.
GRAVITY ERROR
Mercurial barometers are calibrated for standard sea level gravity at latitude 45 °32' 40". If the gravity differs from this amount,their is a error. The correction to be applied to readings at various latitudes is in Bowditch table 12.
TEMPERATURE ERROR
Barometers are calibrated at a standard temperature of 32 degrees. The liquid of a mercurial barometer expands as the temperature of the mercury rises and contracts as it decreases. The correction to adjust the reading can found in Bowditch table 13.
