Originally Posted by
terrymorse
For cumulative altitude gain, Ascent is the most accurate software I've found to date. It usually gets within 1 or 2% of the actual gain on long climbs.
The cumulative number that the Garmin 305 reports is usually too high, so I don't even look at it any more.
I used Polar for several years, and it was consistently 5-8% low. It suffered from barometric drift, especially on large vertical gains. While the Garmin uses barometric measurements, it seems to use the GPS readings to recalibrate the altitude in real time. When I get to the summit of a climb, it's almost always dead on.
FWIW - every single one of my culmulative numbers from the Garmin 305 has been low by 20%-60%. I guess each unit could react differently depending on the barometer, it's quality, resolution and repeatbility itself.