I think I know the answer to my own question, but I hope I'm wrong:
Did the LA River ride today. My new beloved Garmin did beautifully, but. We rode down the river from LA to Long Beach, and took the train back to downtown, then rode again to the start point. I've got the Garmin set up so that it pauses automatically when I stop, and starts up again automatically when I start up again. That is, when the bike on which it's mounted starts moving.
Except that on the train, traveling at 40 mph or so, the Garmin can't tell the difference between my pedalling, and the bike traveling in a train, or on a bike rack on a car, etc. So my stats are all screwed up--I averaged 36 mph!
Is there no solution to this other than to remember to turn the Garmin off when I'm on a train or carrying the bike on a car, and then remember to turn it on again when I resume cycling?
Chagrined in Pasadena,