I did a rollout with each of my bikes and yes, the difference is minimal per revolution, but on a long ride, there are quite a few revolutions--and why even track it if it isn't accurate?

I did a number of wireless computers---I Really liked the features on the Nashbar Tempo (it goes onto pause quickly and stays paused for a long time, it is easy to reset, it displays the basic functions quite clearly, has two wheel diameter, and Nashbar even sells multi-bike kits, so you can move the computer and everything else is already there)---but the freaking sending units on most wireless computers seem to be pure crap.

I have tried a bunch of Sigmas ... have one now ... hopefully this one's sender won't crap out.

Wired? You can good Chinese computers for a couple bucks, as RPenman and others note. Buy a handful and mix and match.

I might go back to Nashbar for the wired version of the Tempo ... but I hate how the wires look, which is pretty silly considering how my bikes look.