On my route the other day I used my "cateye" computer for the first time. (not sure which version, but one of the lower end models). It was installed on the bike by the LBS who sold me the bike. On the ride, I also wore my Garmin Forerunner 310xt on my wrist. This GPS watch is more for running / and triathlons. I've been using the Garmin Forerunner watches for running for the last several years.

I only wore the Garmin on this bike ride to test the accuracy of the Cateye.

I noticed after mile Number one that there was only about a .03 mile discrepancy. I thought, "not too bad.....That's fairly close....."

But after I multiply that by the short 11 mile ride, it adds up..... (11 x .03 = .33)

Here's what they each read -

Cateye -
11.35 miles

Garmin (using GPS) -
11.01 miles

If I were to get up to a 50 mile ride, I'd be looking at a mile and half discrepency.

I was telling a friend of mine this and he said he's heard the cateyes are not "exact".

My questions are -
1. Is it probably an issue with the cateye needing to be adjusted more accurately?
2. is this discrepency just a norm for bike computers and I should pay no attention to it? (this was the view of the friend I spoke to).