General Trip Computer Question

[Dlevy05]

How do trip computers work?

I ask because I was thinking that a difference in placement of the magnets would have an affect on perceived speed, as well as wheel size?

How is the compensation for these variables taken into account?

[rickbb]

If you've entered the wheel (with tire) circumference into the computer correctly, the computer counts revolutions and accumulates distance as revs X this circumference. Mounting position doesn't affect this calculation as long as it picks up each revolution.
You can go twice as fast by mounting two magnets, though. :)

[Dlevy05]

Ahh, good to know. I have never used a comp before, and didn't realize there were setting preprogrammed into my girlfriends' comp when she got her bike.