Altimeter craziness!!

So I purchased the Fenix 6 pro, and really do like it. But I had this nagging feeling I may like the 6X better, so I ordered. I haven't decided which to keep yet but an odd thing has happened. My 6 says I'm at 149ft, my 6X says 62.3 ft. My actual based on google maps coordinates in the place I am standing is 135ft. I calibrated both watches and got the same results at 149ft and 62.3ft. My question is am I calibrating right? What is the difference between calibrating via GPS vs DEM? Should I really just be putting in the altitude manually, and it will stay correct from there? Do I need to calibrate compass first? Thanks, this is driving me crazy!!

  • I would never recommend calibrating by GPS. It is only accurate to like +/- 400 feet. GPS is really good at pinpointing your X and Y coordinates, but sucks at pinpointing your Z coordinate.

    The best way to calibrate is with a known altitude. You say Google Maps puts you at 135ft, so go ahead and calibrate both watches to 135 feet. Problem solved.

    If you don't know your elevation, the next best choice is to calibrate using the DEM file.

    Also, do you have either (or both) in-activity and outside-of-activity automatic calibration turned on, on either or both watches?

  • Lucky youGrinning 

    Your altimeter watch lets you are on the earth. My watch's altimeter shows like I am in the hell - 209 (minus two hundred zero nine). Cold sweat

  • When was the last time you calibrated the altimiter and/or barometer? Did the weather change in your region? Did you travel any significant distances after the last calibration?

    I calibrate the altimeter and the barometer once a few days, depending if there were any rapid air pressure changes. And if the weather is somewhat stable my altimeter stays at around +/- 10m of my real altitude. 

    If I plan to do any activities where I need accurate altitude - I alway calibrate the altimeter (and the barometer if I have the pressure data for the plalce) before the activity.

  • FWIW, I use auto-calibration not during activity (which, I believe, calibrates it once a day, using your phone's GPS coordinates so that it doesn't need to use its internal GPS), as well as continuous auto-calibration during activity, and have had excellent results. My altimeter is never off by more than about 20 feet from what I can tell, and my elevation plots on my activities always look really good. I haven't tinkered with the other settings, or manual calibrations, because I haven't needed to, the watch has been pretty darn near spot-on since I bought it, with those two settings turned on.

  • I have found that auto-calibration not during activity works only if you live on ground level, because it calibrates against the DEM data on the map. I need to add 30m to that to get real data, so that doesn't really work for me.

    I was really confused why my elevation is 30m less than it was before I went to sleep, until I realized that it is caused by the auto calibration Smiley

  • In general: What is the best way (and time) to calibrate the:

    - barometer

    - altimeter.

    And what does auto-calibration do and do I need to turn it on? Eager to hear you opinions...

  • Already answered these questions above :)

  • Yes and thanks for that but for me it's not yet totally clear.

    When I would enter a value in the Altimeter, do I need to do the same with the Barometer or are the two matched automatically? And the auto-calibration calibration option is for me not clear. What does it do and what are the pro's and con's of the different settings? My current settings are:
    - During activity: continue
    - Not during activity: enabled.

    Note: I live in the Netherlands which is unfortunately flat as a pancake, but I would like to measure height and pressure correctly, especially since I want to do some trainings outside the Netherlands (e.g. Belgium).

  • I will try to explain from my experience:

    If the elevation is incorrect, when you enter the correct elevation the watch calculates the sea level pressure against the elevation change. I am not sure how correct that data is, but it will serve as a base line for further calculations when there are pressure changes.

    If you want to be very precise. You will need to find the latest pressure information from the nearest weather station, get the sea level pressure and calibrate both the altimeter with your current altitude and the barometer with the sea level pressure in your area - this will give you the most correct data. But until theare are any quick and/or big changes in the weather or your location.

    The auto-calibration takes your GPS location and adjusts the barometer until your altitude matches on the topographic map.

    If I am in some new place where I don't have the weather data, I would calibrate the altimeter against DEM data before starting any activity.

    The pros (IMO):

    - During the activity it should keep the recorded altitude close to real.

    The cons:

    - Don't know.