Electronics, Lighting, & Gadgets - Calibrate Polar HRM/Cycle Computer

Just got a Polar CS 200 HRM for Christmas and I love it. But...I have noticed that there may be something wrong with the calibration for the cycle computer. It seems to be about 1/10 of a mile off for each mile. I have a route leaving from my house that I have measured many times with both of my cars and my old $10 walmart/schwinn cycle computer. The first ride I took with it is a 10 mile out and 10 mile back and it came up short on the mileage. I have 700 x 23 tires and I entered the correct code...just wondering if anyone else has come up against this with Polar. Thanks.

Sheldon Brown's site (may he rest in peace) knows all, tells all:

Deriving tire diameter from ISO/ETRTO numbers (http://www.sheldonbrown.com/cyclecomputer-calibration.html#iso)
Roll-out Test for Super Accuracy (http://www.sheldonbrown.com/cyclecomputer-calibration.html#rollout)
Using a measured course to fine-tune your setting (http://www.sheldonbrown.com/cyclecomputer-calibration.html#measuredmile)

I've used the measued course method, determining the distance beginning of intersection to beginning of intersection, from Google Maps. When my 3 mile commute goes off by 0.02 miles, I know its time to pump up the tires. I suggest going directly to the measured course method, the longer and straighter, the better.

Thanks, looking on Sheldon's site, I did have another number for my wheels than he had in his charts. I set it and can't wait to try it this weekend.

Just tried it out and it seems to be right on. There has to be something wrong with my mph though ;) I know I was riding. Thanks again.

arent they great? Im using a cs600X and all I got to say is wow.