I just got a new Garmin 1000. Hope the unit is better than the instructions.

First question: I like to keep track of my odometer for maintenance purposes. I have a road bike and a mountain bike. I don't see a separate odometer setting for a second bike. How do I do that?

Second question: How does the unit know my wheel size? I have a speed sensor, but that is useless without knowing my wheel size.

Thanks.