HRM Monitor Frustration

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I don't normally wear it because it's very inaccurate in the calorie count. How can you work out at a modcrate to high intensity and only burn 180 calories. 45 minutes on the elliptical and treadmill combined. It is a sportsline model, if any one has one or can comment I'd appreciate it. I hardly ever go by what the machine says but I also know that I can't have only burned that much. Thanks!!

Aimee