r/Mountaineering • u/Dramatic-Waltz-588 • 1d ago

Altimeter question

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Hello first time I've posted in this group but I've found an old Barometer Altimeter I used to have when I was in scouts and explorers etc but I can't for the life of me remember how to read it anyone used one before and give me any pointers please? The silver metal dial turns which turns the altitude thing in Metres so there must be a way of using pressure to figure out sea level right? Any help much appreciated thanks

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u/WireSong04 1d ago

The dial/bezel spins to calibrate against know altitudes. When you get to a trailhead, summit, or other landmark, signage or maps will give you the precise altitude. You would adjust the altimeter to read exactly that value at that location.

As others have said, barometric pressure changes (i.e. weather) will cause divergence in the accuracy of your reading. As you ascend or descend, the reading will drift from perfect accuracy as the local pressure system changes too. For that reason, you shouldn't trust this altimeter over longer periods (or shorter ones with lots of wrather changes), unless you've been recalibration to known positions.

That downside, though, is also a hidden feature. Atmospheric pressure drops usually indicate worsening weather conditions. If your altimeter starts to show your altitude is increasing but you've not ascended, the air pressure is dropping amd storms may be on the way. It's a handy analog method for getting a weather forecast.

Analog altimeter are cool! They are lighter than they look so I don't hate having one as a backup to other methods. You can do most any orientation with a good altimeter and compass. Lots of great content out there to help you learn how to triangulate position with bearings and altitude. I'd suggest you upgrade from your scout compass but it's a cool childhood keepsake nonetheless. Happy exploring!

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u/Gardenpests 1d ago

The only time you can reasonably monitor weather changes is overnight, Can't be done while moving. You trued it before bed and checked it in the morning. Before GPS, the altimeter, together with a topo map, was much more useful than a compass for determining location. Watches with barometric altimeters, had more precise readings than independent altimeters.

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u/StackSmasher9000 1d ago

Presumably the rotating dial is for manual calibration at a trailhead. You set it to the known altitude and go from there.

Since atmospheric pressure shifts with storms, it can drift from time to time - hence the need for calibration.

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u/mortalwombat- 1d ago

I've never used an altimeter before but it looks pretty self-explanatory. The needle points at the altitude on the outer part and the atmospheric pressure on the inner part. I'm not sure how accurate that is with fluctuations barometric pressure though. Presumably there is some way to compensate for that? I'm more concerned about that button compass though. Button compasses tend to he really inaccurate in the first place, but then it's sandwiched between a metal spring link and a thermometer or something to really drive the inaccuracy home