What's the use of using altimeter when barometer shows altitude too?

[Rindert]

Hey you guys (and girls?),

I've just purchased a Suunto Core black/yellow for my coming trips to the Alps. I happen to absolutely love it.

Just find it quite difficult to understand the difference between baro and alti mode. The manual says that:

- barometer uses absolute air pressure + altitude reference
- altimeter uses absolute air pressurre + sea level pressure reference

However, setting the altitude reference does not only change the barometer readings, but also a changed altimeter reading. Moreover, changing sea level pressure reference results in a changed altitude, but also in changed barometer readings. What am I missing here? what don't I understand? Can somebody help me with understanding this?

Last question: the barometer also shows altitude measurement. What is the use of using the altimeter then when climbing?

Don't want to come across like a complete moron, but I just don't get it. Thank you for your help!

Rindert

	Suunto Visit SuuntoWatches.com to see Suunto's full line of wrist top computers and compasses.

	Suunto Core - Click for more info The Suunto Core is the benchmark of Suunto's ABC (Altimeter, Barometer, Compass) wristop computers, furnishing the best features of top-selling Suunto predecessors, and then advancing upon their legacy with innovative environmental monitoring functions that any outdoor adventurer will find invaluable. The Suunto Core is the culmination of years of testing, research, user feedback from the field, and technological advancements in the Suunto laboratory.

[mnf63]

In the end all the watch does is measure the air pressure surrounding it. It cannot interpret that pressure unless you either tell it what atmospheric pressure at sea level is (in which case it can then work out your altitude) or you tell it what altitude you are at (in which case it can then work out what atmospheric pressure at sea level is). Actual pressure at the watch, atmospheric pressure at sea level and your altitude are all related - if you know two you can work out the third.

e.g. The watch measures a pressure of 1010 hPa. It could be that you are at sea level and this is atmospheric pressure; or it could be that atmospheric pressure at sea level is 1020 hPa but the pressure around your watch is reduced by your altitidue of 85m. You have to tell the watch either the pressure at sea level or your altitude (which you will have to know from other sources) before it knows the situtation.

In the end: if you tell the watch what atmospheric pressure at sea level is (in "reference" setting) it will work out your altitude; if you tell it what your altitude is (in "reference" setting) it will work what atmospheric pressure at sea level is.

Finally, the altitude that the watch displays in "barometer" mode is the reference altitude you have set and will remain constant. In "barometer" mode the watch will asssume that you are staying at the same altitude and that any change in air pressure around it is due to atmospheric pressure changing. So, if you climb in barometer mode the watch will assume that the reducing air pressure around it is due to atmospheric pressure reducing. It will assume your altitude remains at the reference altitude you have set.

Hope that helps.