Elevation on watch vs MapMy app

lorrpb

So I got both my watch and app set up and started at the same time for yesterday's bike ride. (Amazing I know lol.) My Garmin VA3 gave me 256 ft elevation gain and MapMyRun/bike (on iPhone) gave me 850 ft. Is this absolute difference vs cumulative gain or what?

AnvilHead

MapMyRun is using GPS elevation data, your VA3 is using a barometric altimeter to determine elevation. In either/both cases, the figure it’s giving you is your total ascent during the ride.

NorthCascades

The barometer in your watch is probably closer to the truth. Try turning elevation corrections on and off (in Garmin Connect) and see what that says.

lorrpb

I looked into this on google and found tons of complaints about VA3 barometer not working correctly. I also noticed that it had me biking underwater half the time and the ending elevation was about 30 ft higher than starting.

NorthCascades

@lorrpb

You need to think of a barometric altimeter as two different things. Really it's one measuring instrument with two readouts.

It measures air pressure (and temperature) to figure out how high up you are. That works pretty good because there's more air pressure down low than up high.

But going up and down isn't the only thing that can affect air pressure, the weather does too. Air pressure is higher in some places and lower in others, that's what makes wind, air rushing from a high pressure zone to a lower one to equalize. People use barometers for basic weather forecasting, if the pressure drops a lot quickly, a storm is probably moving in.

So there's an obvious problem with all of this. Your watch has no idea if the air pressure is changing because you're moving up or down, or because of weather.

To get the best accuracy out of a barometric altimeter, you should calibrate it regularly. Because every one ever made suffered that kind of drift.

But even without accuracy, they still have very good precision. Better than GPS. Meaning the total cumulative elevation gain is often very close to correct even when the absolute numbers are off.

NorthCascades

One more thing.

Go to Garmin Connect on the PC. Pull the ride up. Scroll down, a little before the map on the right, near the list of gear you used. You'll see the text "elevation corrections: disabled." Click disabled, you'll get a menu, hit enabled. The page will refresh and you'll get a fresh set of numbers.

I suggested this before but I forgot there's no way to do this in the app.

lorrpb

Thank you. I was actually searching to find out how to calibrate it when I found all the other posts. I was on my mobile devices, not PC, so I will check that next.

lorrpb

Hmm, I do not see the option you describe.

NorthCascades

Scroll the page down a little, and look on the right. I'm on my phone so I can't take a screenshot at the moment.

lorrpb

Found it, thanks! At least it has me starting and ending at the same elevation. Does it use a 'relative' elevation such that your starting point is always 0, then + or - from that point?

NorthCascades

The elevation correction thing takes all the lat/lon data in your recording, and looks up the elevation for that point in a database that came from USGS.

lorrpb

OK, I guess it did adjust it. It was confusing because the scale still says -250 but all the recorded elevations are now above sea level. Thanks for the tip.