GPS elevations
 

Have a newer Garmin GPS (Astro 320, essentially like the 60/64 series). Use it to track hikes, but have been a bit suspicious of the total elevation gain numbers it has been giving me. On a long slow logging road slog the other day, all downhill at a slow grade, it told me I actually gained a few more metres... Seems to be fine with distance. Anyone had this experience and know a fix? Turn off the auto calibration? Force to get elevation from GPS instead of barometer? Be a bit hassled by using barometer and calibrating myself over a hike with start elevation, peak elevation etc?

Or, I could just ignore it and feel like I am working harder than I am because it bulks up my elevation gain by a few hundred meters over a day?

This is pretty common. If it is logging very frequently, then little errors can add up.

E.g. imagine that you sit in the same spot all day with the GPS on and it takes 1000 measurements. Due to the normal errors, the readings are a little scattered within a 5 meter cube. If you ask it how much you moved it might say you actually covered a fair amount of gross distance and elevation gain and loss because it thinks you were going up and down and side to side all day.

Here is what I usually do:
- Take the tracks into my computer.
- Filter it down to a more reasonable number.
- View in Google Earth and use the stats there.

Sometimes I will even just take the start and end elevation numbers if I know it was almost entirely up or entirely down.

I have a Garmin Oregon 450. It regularly overestimates the elevation gain, especially on more complex trails (so not simply straight up or down). When I download the track to my computer (Basecamp), however, all this extra elevation seems to disappear and matches up quite well with the actual elevation gain. I always thought this was a bit weird, but never looked into why.

Almost all GPS programs have a way of cleaning your track, which should get rid of most of the noise. All the devices I've ever used insert some random side tracks every once in awhile that can add up to many vertical and / or horizontal meters. My altimeter watch used to be really bad in strong winds too - adding up my elevation gains far beyond what they really were. It made me feel very accomplished tho... :P