I don't have the manual. It has disappeared. . . . . They did say they'd photocopy the instructions for me so I'd have them. I forgot to do that while I was there yesterday. Must remember today!
Just download the manual:
http://www.cateye.com/en/tech_suppor..._downloads.php

You'll need to reset it each time you replace the battery so you need the manual. Just save it on your computer.

More info on wheel measurement:
http://www.sheldonbrown.com/brandt/circumference.html