The CycleOps Power PowerCal uses heart rate to calculate power and then sends both heart rate and power numbers wirelessly to any ANT+ device or ANT+ enabled head unit. Already have a Garmin but don't want to spend thousands of dollars on a power meter? The PowerCal is an effective solution for the budget-minded rider. It is also a great fill in for the PowerTap hub when you decide to use a non PowerTap wheel.
The PowerCal system is based on research done by CycleOps in conjunction with researchers at the University of Colorado Boulder. CycleOps and the University staff spent years reviewing the relationship between power output and heart rate. What they found is heart rate mirrored power in a very consistent and predictable pattern. They fed that data into the PowerCal system.
Very poor results. I had a wired powertap and it was very good but broke. I bought this because I read a review on how great it was and how it mirrored the Powertap (within reason). I did a test were I go up my usual hill at a constant pace and keep about 300 watts. On my powercal I got ranges of 45 watts to 1730 watts. It is so inconsistent that it is basically useless. I used it with my garmin edge 500. I have used my powertap enough in the past to pretty much know my wattage and this basically was never close. I would tell people that you can't get something for free. Sorry but you can't mirror power using your heartrate no matter what dr lim says. It just doesn't work. If there was a zero star I would have rated it at that.
Cons: This isn't a power meter, it is not reliable
This is a great product to guesstimate your power output. it is meant to introduce people to training with power with out breaking the bank . If you shave your legs or cut the tags of your jerseys to be lighter then this is not for you. It's about 5 to 10 off at times but for the price it can not be beat.
Pros: Inexpensive. Portability,
Cons: Not as precise as SRM or powertap