In reply to TheDrunkenBakers:
> (In reply to Martin1978)
> [...]
>
> I should qualify that the Ambit is a GPS watch and so all measures are downloaded including ascent/descent so I'm assuming that this is calculated in the output.
Ok, even more than very accurate then
I have done and seen results of tests comparing HRM results against those from gym equipment. The gym equipment does not (in this case) measure heart rate but does calculations based on speed, distance, resistance, age and weight. These are the same factors and calculations most "average" figures for calories burned will use (i.e. the 100Cals/km)
Introducing heart rate into the equation (by a HRM, chest strap or hand grips) changes the results (calorie burn) significantly, by as much as 30%.
Reason?
The calculations without heart rate can't take into account an individuals efficiency or effort in terms of: oxygen delivery, cooling the body, breakdown of energy, clearance of waste by-products, etc etc.
I accept that heart rate is still a predictor of these things, but there are many studies that show that it is a reliable predictor of how hard the cardiorespiratory system is working (in that it reacts predictably to the above factors).
A simple example: Journey price calculator tells me that my car will do a trip to Keswick and back on £28 of fuel (calories). That is a pretty good estimate based on average mpg for my car and an average driving style, average conditions, medium traffic, etc. It doesn't know my true, actual mpg though. This would make it even more accurate, especially if there was a faulty sensor, I was towing, poor quality fuel, had the AC on, or that particular journey was all up hill.
If I inputted my actual mpg from the trip computer when I got home, the cost of the journey (calories) would be far more accurate. This is what sticking your heart rate into calorie calculations does.
Or simply, you have an expensive bit of technology and bought it for a reason. 25,000 Calories is a good reason to smile. Enjoy the next 25,000