I use a Specialized basic wired computer on my front fork. At first I didn't know if it helped or hurt because I always try to mess with it and it kept my eyes off the road. Now I just look at it at breaks or stops.

It would be nice if it had a back light. However the little watch battery lasts 3 years, can't complain.

One problem I have is how to be accurate on the circumference entry? The manual says for 700 x 23/25c you use 214cm but I did a rollout on my own and measured 210cm. Does that kill my accuracy if I pick one or the other?