Fenix 6s Pro Altimeter wrong by 50 meters. 2526827 over 4 years ago. Hi, I have tried calibrating my altimeter for more than 5 times in the past week. I have done it manually by entering my altitude above sea level from Google maps which is 57 meters. Every night I check the altitude and it goes way off from 90 meters to 15 meters. The altimeter is alright, especially if I lock the sensor to altimeter mode and periodically calibrate the elevation using GPS or manually upon arriving at known elevations. It's not always accurate, sure, but afaik that's an expected behavior of barometric sensors. If I were you, however, I'd rather ask myself if the Instinct is the right Best Garmin for Triathlon. Key Features. Our Rating. Garmin Forerunner 935: Advanced running and multisport features, Built-in barometer, altimeter and electronic compass, Advanced dynamics for running, cycling and swimming, Built-in activity profiles ★ ★ ★ ★ ★ Garmin Fenix 5 Plus I agree with this being a clear Garmin fault. Air pressure changes all the time. Most of the time it is not a drastic change and if so, the Garmin watches can have a storm alert feature. So, why can't the altitude be more dependent on GPS location? This morning, as I always do, I drove 22 miles to work in the North west of England. According to several websites there is a difference in altitude between my start and finish points of circa 220 feet, the altimeter on my Fenix 5 shows no difference in altitude at any time in the last 4 hours. I recently bought a Fenix 5 Plus (my first Garmin watch). I've been a consistent runner/cyclist that used strava in my phone to record my activities. I was quite excited with the new elevation accuracy i would get from the altimeter until i went on my first run and noticed that the starting point from where i start all my runs was up by 80 Garmin Fenix 5x here. I had a similar problem, now I manually calibrate the height. I turned off automatic calibration using GPS. And most of the time it shows the correct measurement, except when the barometer starts going wild because the altimeter moves as the barometer works. I started today at 2100m, climbed up to 3200m (at home moutains, 100% sure values are correct) and Garmin says that the elevation gain is 720m. It happens only in backcountry ski mode, I made the descent with hiking mode and it calculated the elevation loss properly. My Fenix is updated to the latest firmware versione. Any idea? JLqZZ.