I bought a Sportline HRM at target ($50.) a few weeks ago and have been going by what it said. Big mistake! I was a little suspicious because it was way higher than the eliptical machine at the gym. For instance My hrm said 780 burned in one hour the gyms machine said 546. Yesterday I bought another hrm. This time I got a polar F6 because I had been reading so much about them on the site. Here is the Skinny on my adventure. I get on the scale this morning and I have gained 2 lbs in the last 2 weeks. I went to the gym this morning and used my polar HRM and it said 445 burned in 1 hour! that is a huge difference for me. That means I have been eating close to 300 extra calories a day. I workout 6 days a week so it's not a wonder that I gained. But I will not be discouraged. I will trust this new one and hope it works. Something has to work. I'm starting to feel like I'm in a nightmare I can't get out of. I will not give up though. Has anyone else had a similar experience with their hrm?