A quick tutorial on millibars & stuff for those who keep asking:

[karlrschneider]

The measurement 'millibar' 1/1000 of a bar is simply a unit of atmospheric pressure...how much the air "weighs" over any given point.

"Standard" sea-level pressure is 1013.25 mb, or expressed another way, 29.92 inches of mercury, or about 14.7 pounds per square inch. (the STP or standard pressure & temp includes this figure as a worldwide average...the temperature is considered 59 deg. F)

As you go up the pressure generally decreases about an inch of Hg (mercury) per thousand feet, approximately. A bit less...the altitude at where the air pressure is HALF of standard is about 18,000 feet.

This info is easy to Google but we seem to have a lot of DUers who haven't figured it out...
:eyes:
I've taught meteorology for flight schools for about 40 years, feel free to ask me (PM or email [email protected]) if you have more questions.
;-)