I now have a Garmin Edge 510. The local bike shop, a Specialized Concept Store, kindly priced matched against the going online price for me. They get the sale and I get a good price.
I had found on importing my rides into Strava that the altimeter reading can be quite noisy. I wonder how it handles things like vibration and the effect of moving air. The noise amplitude is a few feet. If we consider the tiny change in air pressure this would seem quite good. It can seem to confuse Strava. Most notably my “biggest ever climb” is a lot smaller than climbs I have done.
The image shows a short ride picking up my child from nursery today. I rode with him on a child seat so was travelling around 20mph before fetching him, 12mph with him onboard. I found that I could power the unit off while it was paused, then resume the ride later.
Making this picture has restored my confidence in the 510. The altimeter does drift over time. I understand Garmin Connect can correct that for me. It does seem to give a reasonable representation of the ride over time periods of interest for a climb.
I can use a reference point to correct the initial altitude. I have one set up, but it did not match. It seems that the accuracy of the initial GPS fix is quite low, so both my reference location and my actual ride start location have some error. I need to re-record the reference location having allowed the GPS accuracy to settle down. If I power off the unit then the altitude will drift. I wonder if it uses the GPS reading to set initial altitude when powered on again, even though it is resuming the ride where it left off.
One thing that has surprised me riding with an altimeter is how slow climbs and falls add up. I’ve double checked on a map that two places I thought were at vastly different heights were at the same height, but I climb a short steep hill before slowly descending when travelling between them. The gradients in the right segment of this graph I consider pretty flat.