How often to recalibrate altimeter/barometer on Ambit?

[JPfeuffer]

Hey guys, happy weekend! Just was wondering how often you reset/calibrate your altimeter n barometer on your Suunto's specifically the Ambit but I"m curious about other models as well. Yesterday I checked in on my local weather website n plugged in the current barometer readings of the day which were 29.90 just to make sure everything was right before I left for the day. I headed out into the city came home to find it remained the same at 29.90. Woke up this morning and checked in with my local weather n the Ambit was still reading 29.90 but current local readings was 29.82. Also, the altitude changed by 100 feet when I got home. I was all over the place yesterday, in Jersey, in towers in Manhattan and below sea level in the tunnel but living close to the city the temperature n weather conditions were pretty much steady wherever I went. So would it be normal for the alt/barometer to get "confused" with all the places I have been through out the day and normally need calibration for the next venture out the door? So it seems to me if you want accurate readings, would it be necessary to find points to calibrate when at various altitudes n locations all day long?

[cobrapa]

It depends! If air pressure is changing due to high pressure/low pressure systems moving through, and you want accurate readings, you'll need to reference it more often. Do you understand why the altitude changed by 100ft?

[Lost-again]

To be honest the sea level pressure comes calibrated from Suunto, so in most cases you should never need to re-set it. I never have on my observer, x9 or Ambit. I don't bother re-setting the altitude day to day, it wil naturally drift with the weather, even if you put it in auto mode. I just zero the reference it to a known altitude when I intend to use it for outdoor activity or a run. The rest of the time I leave it in Baro mode to keep an eye on the pressure trend and monitor the weather.

[JPfeuffer]

I can understand w the air pressure changing so I will have to agree n say that must be what it is. Because at other times its incredibly accurate in altitude readings just doesn't seem to be highly accurate for too long of a time and I guess that can be w the changes of pressure. BTW, just got back from a trail hike that started at sea level for the first half a mile then we started climbing which we topped out at 195 feet. I calibrated the sea level once again because when I got there it was reading about 35 feet at sea level. I set it to 0 and walked along sea level which was staying accurate from 0 to 7 feet all the way. It accurately read the correct altitude of the trail we climbed but then we got back down to sea level to where I originally set the watch at 0 feet and 2 hours later...and it was reading 30 feet again. As long as this is not out of the ordinary I can live with this. I mainly purchased the watched for logging times and distances on runs w the GPS anyway.

[Lost-again]

I always use meters so the drift looks smaller . 30 feet is quite normal if the weather is changing, anything up to 100 feet over the day. It is unusual to get more than this unless there is a storm moving through, but if you leave it in alt mode for weeks it can drift a lot. If you re-reference it every few hours when you reach a known alt you are never far off. Although I often don't touch it all day if the weather is stable.

[paduncan]

Hey guys, happy weekend! Just was wondering how often you reset/calibrate your altimeter n barometer on your Suunto's specifically the Ambit but I"m curious about other models as well. Yesterday I checked in on my local weather website n plugged in the current barometer readings of the day which were 29.90 just to make sure everything was right before I left for the day. I headed out into the city came home to find it remained the same at 29.90. Woke up this morning and checked in with my local weather n the Ambit was still reading 29.90 but current local readings was 29.82. Also, the altitude changed by 100 feet when I got home. I was all over the place yesterday, in Jersey, in towers in Manhattan and below sea level in the tunnel but living close to the city the temperature n weather conditions were pretty much steady wherever I went. So would it be normal for the alt/barometer to get "confused" with all the places I have been through out the day and normally need calibration for the next venture out the door? So it seems to me if you want accurate readings, would it be necessary to find points to calibrate when at various altitudes n locations all day long?

This is purely compulsive (and I do it also) - here is what I do.

In Alti/Baro screen, I set the bottom view to read the ref. altitude. If I see the ref. altitude somehow creep even in auto mode, I just set it back again to the known ref. altitude. If you are out and about and you are in alti mode, the only way that the altitude will remain 100% accurate is if the air pressure stays constant (i.e., steady weather conditions). If the air pressure changes AT ALL due to weather (a high pressure system moving in or out, or a low pressure system moving in or out) your altitude readings will change (for example if you are comparing your altitude when you start out a hike vs. when you finish).