When I set it up, before I'd clipped it on, it showed 450 calories burned. Is that, like, a BMR estimate based on the time of day, or is that a mistake?
I'm not sure... When I set mine up, it was totally blank. Try holding the button down to reset the time measured for the day to start now. You'll have a more accurate reading, at least, but online it'll still track those 450 calories, but they won't show up on your Fitbit as you read it through the day. You can just subtract those 450 calories from what online says at the end of the day. That's what I'd do at least! Mine automatically resets at 0 everything at midnight everyday.