Quit trying to get around it - it doesn't work. Two riders - same age, fitness, etc. - can have a 30 bpm difference. The HR of the same rider changes depending on humidity, hydration, time of the ride, amount of riding in the last week, amount of sleep, stress level at home or work, and on and on. HR cannot give you Calories.

I'm surprised some legal shark hasn't picked up on this for a class action suit - millions of Garmin buyers have been lied to. Should be some big money in it.