Isn't that going the iBike (?) approach? Thing thingy that measures wind resistance and all' date=' and is pretty much universally denounced as useless... [/quote'] Yes the i bike thingy was a good idea but (i believe and stand to be corrected) relys on the measurement of airflow, which as we can be rather iffy. What I was suggesting was not to measure airflow but to rather use the effort as recorded on a hrm and convert this to watts. Power measurement and recording is obviously more accurate by the use of strain gauges or other mechanical devices that react in relation to the "power" appllied, but they are not cheap especially when you try to fit them onto weight concious bicycles. Therefore I was wondering about a conversion factor being incorporated into a HRM software using the already vast amount of power VS heart data that has been gathered over the last few years. Granted it might not be 100% accurate (how do you know for sure your current power device is 100% correct all the time), but as long as it remains consistent, this would be cheaper than the available options of power measuring devices. I feel where you're going SwissVan,there are just to many variable variables in you're equation,if I can put it like that.The missing ingredient here is GPS.Think about it,GPS provides incline,that should make it significantly more accurate.Mmm,maybe. I think the peoples in the biz(Polar) would of done this if feasible.They give us the next best thing.Hart rate & Kcal's!