Lou Holtman writes:

wrote:
On Apr 16, 12:42 pm, Jason Spaceman
wrote:
I noticed that one of the Paris-Roubaix riders used a Garmin Edge 305
GPS/cyclocomputer yesterday (seehttp://tinyurl.com/2hyjfm).

Has anyone tried these? How do they calculate altitude data? Using
GPS, or using some sort of barometric sensor to measure changes in air
pressure? And which would be the more accurate of the two?

Also, does the Edge 305 record your route and let you download it
afterwards and plot it with Google Earth?

J. Spaceman

A freind of mine has one. It uses both to determine altitude, but he
complains it does not have a manual calibration feature. Like he knows
how high his house is, but it always tries to do it itself, and since
his rides start out with some immediate up and downs, and weather
shifts, it takes a while to for the altitude measurement to settle
down and sometimes is off a bit.

Joseph



Yes that's very annoying. You have to wait for about 1 minute before
it displays the correct altitude.

Depends on how you define "correct". I've recorded the elevation for
an hour with the unit lying in my backyard. The result was, more or
less, a periodic sawtooth. The amplitude was around 10-20 meters,
which, I suspect, accounts for its optimism on accumulated climbing.
I assume this is due to the motion of the GPS satellites.

--
Joe Riel