Logging Tour Vert Geek-ery Questions

So here's a question about device accuracy when measuring vert gained/lost during a tour and the elevation accuracy of tour planning tools in general (i.e. Nat Geo, etc.)

So did this nice tour from the top of Chair 8 at Baker (started elevation log here) out the Arm beyond the drop in for the Hourglass (lots of up and down travel), skied south into the "East Fork" of Swift Creek (for lack of a better name). Skied three more runs in the Ann vicinity (great snow btw), climbed back up to the Arm and skied the right side of the Safety Line back to Chair 8 (stopped log back at WS parking lot).

Pretty simple.

My Sunnto Vector logged the tour at 5140' of gain.

BC Nav app on Samsung Galaxy 4 logged the same tour at 4344' of gain.

Exporting the gpx track from BC Nav and importing into Nat Geo (older version) - the elevation profile of the track in Nat Geo shows 4630' of elevation gain.

Pretty big difference I think. Which one is right-er?

This isn't the first time I've had some elevation gain discrepancies of this size between watch and phone gps/mapping app, but those tours had way more elevation gain/loss and much larger variations in elevation (like the Watson Trav).

This tour is much smaller, is in a fairly narrow elevation band (less error in watch altimeter?), and has a shorter duration - 6:29:21 to be precise versus the +12 hour day for the Watson (also less time for changes in air pressure due to atmospheric change).

Please help, my fragile ego is hanging in the balance . . .

Under open skies I would probably trust the GPS over the barometric altimeter unless you were calibrating it regularly.

I have the Suunto Ambit2 which uses both GPS and barometric altimeter to determine altitude. I imagine it calibrates using the GPS when the signal is good and falls back to the barometric altimeter when it goes poor. In my experience it is quite accurate.

I've wondered about recalibrating, but then thought that recalibrating in middle of recording an elevation log would artificially add gain or loss to the log since you are manually changing the elevation.

Another thing is the Sunnto always records greater elevation gain. If it were an issue of elevation I would think it would be off either direction (either more or less gain recorded).

The fact the watch always records greater gain might also just be a function of how the watch always 'decalibrates' over the course of a tour.

Finally, I've noticed the watch doesn't necessarily decalibrate but loses accuracy in elevation with a gain in elevation but then regains accuracy as I return to the starting point.

For instance - on a summit ski of Baker, if I set the watch at 3700' at the Glacier Creek TH it will be hundreds of feet off at the summit, but then be right back at 3700' upon return to the TH. I wish I had kept track of which direction the watch is off on the summit . . . .

Would be stoked to hear about how phone GPS elevation compares with handheld GPS elevation. Meanwhile I'll just ask the oracle and see what comes up . . .

GPS elevation is much less accurate than lat/long position.

However, some phone systems will correct for elevation after the fact, since if you know lat/long accurately, and have a good elevation database, you can figure out what your elevation was.

I use RideWithGPS (designed for cycling), and upload the days tracks. It corrects for elevation after the fact, and I consider it to be a pretty accurate record of the vertical feet. It doesn't count runs or other fancy stuff but works for my purposes.

Not that snow depth is an issue right now but later in the season there could be 40' of snow in specific places. I don't think the GPS data can correct for that since it is using historical measurements presumably based on the conditions in which the measurement was taken unless the device is trying to triangulate in 3 dimension in which case I've heard the same thing about GPS having poor accuracy for altitude.

I think the issue that you're having is probably related more to the measurement resolution (frequency and precision) rather than accuracy of the devices. I recently bought an InReach and don't have much experience with it yet but it only reports position every 10 minutes which basically cut the reported mileage of a recent trail run in half since it missed a lot of switch backs in the trail.

OP: why don't you post the .gpx so we can see what's in there? If you pm me I can post a link here to it. How many points are in the file? Are elevations listed in the .gpx? If you overlay the .gpx on the map, does the drawn path actually go where you went? As others have said if the gps is recording your position infrequently you might miss some elevation if you travelled both up and down between recorded points.