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Forerunner 405 elevation data

Joined: 04 Jun 2008
Posts: 18
New York, United States
Posted: Tue 21 Jul 2009 11:58 am GMT   topTop
I posted a similar message in another thread, but I thought this deserved its own discussion. Has anyone else found that the elevation data from Garmin's Forerunner 405 are way off?

I bought a 405 about three weeks ago. For the most part, I like it, but the elevation data were way off. When I went up a small mountain outside town (elevation gain 900 feet), it'd tell me I gained 2000+ feet in elevation. I exchanged a bunch of e-mails with Garmin over this, and we concluded the device was defective. So I traded it in for a new last Sunday. I've tested the new one twice, and the elevation is way off on this one as well. I took a three-mile walk around my neighborhood last night (can't run; hurt leg), and 405 tells me I gained 800 feet in elevation, the equivalent of climbing a small mountain. And the roads are mostly flat.
Joined: 24 Dec 2007
Posts: 7
Colorado, United States
Posted: Tue 21 Jul 2009 02:34 pm GMT   topTop
Yeah, the elevation of GPS is pretty suspect. They do pretty well on the horizontal, but vertical not so well. That being said, 1100 feet seems really bad! At any one point they can be as much as 200' off, but it shouldn't be cumulative! did the elevation profile look ok? I typically find that the profile function works pretty well, but I haven't double checked that against what the "total elevation gain" tells me.

what it's probably doing is calculating the change in elevation error at every point, but then averaging it for the run?
Joined: 04 Jun 2008
Posts: 18
New York, United States
Posted: Thu 23 Jul 2009 02:19 am GMT   topTop
The elevation profile looks OK, but the data in the report is wrong. Today, for instance, I went up a small mountain with about 850 feet in elevation gain. It tells me I gained 1,500 feet. Yet the profile looks fine.
Joined: 28 Aug 2009
Posts: 8
California, United States
Posted: Thu 10 Sep 2009 11:57 pm GMT   topTop
I'm suspicious of the total ascent reported by my 405. Generally the elevation profile looks about right, though I do see a few dips on routes where I know they aren't there. On the mountain race I did on Labor Day, my 405 reported 5442 feet total ascent; the race goes from 6000' to 10,064', with only a little downhill, billed as a little over 4000' by race director. I guess I'm in the camp with doubters of the 405's vertical accuracy.