barometric pressure

[mattaxelrod]

Does a regular barometer reflect changes due to altitude? If my barometer reads about 30" at sea level and I bring it with me in the cockpit, does it read 25" at 5000', or do they have some built in adjustment for altitude?

Just wondering,
Matt

 

[Henning]

Does a regular barometer reflect changes due to altitude? If my barometer reads about 30" at sea level and I bring it with me in the cockpit, does it read 25" at 5000', or do they have some built in adjustment for altitude?

Just wondering,
Matt

It will read the ambient pressure wherever it is. It has no idea of what altitude it is at so it has no way to compensate. That's why we get the baro setting from the ground, because they know what altitude they are at so they can read the pressure from the kollsman window.

 

[gismo]

Does a regular barometer reflect changes due to altitude? If my barometer reads about 30" at sea level and I bring it with me in the cockpit, does it read 25" at 5000', or do they have some built in adjustment for altitude?

You mean like a GPS or radar altimeter?

Seriously, the answer to your first and second questions is yes. An altimeter is simply a barometer that's calibrated to read in feet above sea level and usually includes a way to easily compensate for local variations in sea level pressure.

Most any barometer, conversely has an adjustment to compensate for altitude so it reads sea level pressure (or more acccurately, atmospheric pressure compensated to show what the pressure would be if you were at sea level.

 

[BruceAir]

The Web (and Google) is a wonderful thing: http://www.barometerworld.co.uk/

N.B.: http://www.barometerworld.co.uk/FAQ.htm

 

[Bones]

Good point steve...above FL180 everyone uses 29.92 for a few different reasons but thats one of them!

 

[Ghery]

Good point steve...above FL180 everyone uses 29.92 for a few different reasons but thats one of them!

And while you're sitting the back of the airliner with the moving map display showing "altitude", we pilots know that is a fiction. 39,000 feet? FL 390 I believe, but if it really is 39,000 feet, someone got lucky. Oh well...