BAROMETRIC PRESSURE -- Kristina Gollwitzer of Wellsboro, PA noted that she has been trying to understand the difference between barometric pressure, sea level pressure and absolute pressure. She is trying to set up an electronic altimeter/barometer to use on hiking trips. The device doesn't display actual barometric pressure, but rather sea level and absolute pressure.

First, I suggest you read the question immediately preceeding this one about pressure in the mountains.

Next, I think that "absolute pressure" is the same as barometric pressure. It is whatever the pressure is where you happen to be.

The sea level pressure (as in the previous question) involves a conversion from your altitude to sea level. The device likely takes the pressure it is reading and assumes a "standard atmosphere" temperature value (not the actual one) beneath that point. Using a built in formula or algorithm, it does the conversion to sea level and also generates an "approximate" altitude for your (hence the term "altimeter").

There will be some error in this conversion. But unless the atmosphere is very warm or very cold, both the sea level pressure and the altitude the device provides should be useable.

© How the Weatherworks (1997-2006)

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