I have a follow up to my initial report, and can now join the group of concerned owners. Today, during my P90X workout, the heart rate struggled to get a heart rate, and showed my rate in the 60s when I was clearly well into the 150s and beyond. It was during Cardio X. Seems when I moved my watch back further on my arm, and further from the end of my wrist, the heart rate jumped back. I do have arm hair - not too hairy, but normal dude hair. That concerns me. I'm certainly not going to shave that part of my arm. I'm wondering if it's sweat-related, or hair-related. Anyone else venture a guess?