In reply to featuresforfeet:
>Yes, cycling up a fairly steep hill (8%) for an hour as fast as I could manage.
Were you also using an Odometer on the bike? If they both transmit with analogue signals, I'm guessing you could have potential for interference, especially when you lean forward/crunch while going uphill.
If you were cycling for an hour and you hit 220+ for any useful period of time, then I'd imagine you'd need to take a wee break to recover
Either that, or you encountered a very steep incline right at the end and really went for it, in which case I'd be pretty pleased with myself, if I was you, for that kind of effort.
Personally, I'd check for interference first, secondly dismiss as an erratic reading, or if you really want the bragging rights, try and repeat the feat (but remove the odometer and any other electronics first).
D