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Total Ascent Difference

FelipeSerra
over 5 years ago

Hello, today make a ride with a friend, he has Edge 820 and i have 830. The total ascent between both devices show significant difference.

Edge 820 --> 1979 mt.

Edge 830 --> 1836 mt.

Here's the activity, https://connect.garmin.com/modern/activity/4660215889

when i correct elevation, total ascent now shows 2112 mt.

I was using GPS + Glonass, Latest beta and GPS 2.90

Any ideas?

Regards,

FElipe

  • 0 over 5 years ago in reply to dpawlyk

    Given the complexities of using pressure to calculate altitude I'm impressed how accurate the result is. I've seen some weirdness when the weather changes dramatically but equally I've cycled past altitude signs and been within a couple of metres of the displayed value which really is remarkable.

  • 0 over 5 years ago in reply to jgforrest

    The accuracy of the gain result is not dependent on the accuracy of the absolute elevation result.

    That is, the gain can be accurate even when the absolute elevation is off (by a constant amount).

  • 0 over 5 years ago in reply to dpawlyk

    Actually, if you want to be precise, this is not correct. The air pressure in function of the altitude is an exponential function - see e.g. Wikipedia. That means that the change in air pressure corresponding to an altitude gain of e.g. 100m really depends on the altitude where you start from. The other way around, a certain change in air pressure may mean 100m altitude gain if starting from an altitude of 1000m, but it will be some percents more if starting at 2000m.

    But in practice, I'd guess that you'll hardly notice the difference on the Edge or similar devices, due to the tolerances on the barometric sensors - as long as the absolute elevation setting on your device is not way off from reality.

  • 0 over 5 years ago in reply to Chutin

    The response of the device to air pressure has to be accurate (which is what you are talking about).

    The devices let you "calibrate" the device to a known elevation but the amount that is likely to be off isn't likely to change the gain results at all.