Ditto to the advice above. One other thing to consider, and it may or may not apply to your situation. I found that my wireless computer created interference with my heart rate monitor and gave me faulty readings. So, if you're using a wireless computer, try the monitor with the computer off the bike.
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A conclusion is the place where you got tired of thinking. - S. Wright
Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831