The PowerCal is a strap with an algorithm that converts your heart rate into an ANT watts signal. This can then be displayed on compatible computers, such as the Garmin Edge of CycleOps Joule.
On the plus side, it quantifies your effort on the bike, providing a real-time 'wattage' number as you ride and allowing for a full measurement of effort in any number of power software options.
On the negative side, it isn't a power meter. The PowerCal doesn't measure power, it guesses it, and in doing so doesn't provide any realistic semblance of accurate power meter data.
For years, CycleOps has done a great job of providing reliable hub-based power meters at a reasonable cost. The PowerCal is an attempt to bring in some new customers at a very low relative price.
Part of the problem is simply presentation: if the PowerCal showed information called something besides 'watts' it could be more useful. Just look at the Nike FuelBand.
Quantifying effort without a real power meter is tricky. Strava has addressed this with a Suffer Score based on time spent in various heart rate zones. In the parallel field of running, TrainingPeaks has used a Training Stress Score based on time over pace, taking your top-end speed into consideration. And the iBike has undertaken to measure most of the forces opposing a cyclist, and doing the math to spit out a wattage number.
In a number of trials with the PowerCal, we found the 'wattage' numbers to be way, way off, both in the short term and averaged over 90-minute rides. Also, the corresponding summation metrics, such as kilojoules or Training Stress Scores, were also off by about 30 percent compared to files from the same ride with a power meter.
In TrainingPeaks, PowerCal's number changes were much more drastic
There's no way to adjust anything in the PowerCal's algorithm. Whether you're a 20-year-old fit woman or an 80-year-old man with one leg, the PowerCal spits out the same wattage number based on fluctuations in heart rate.
The concept – quantifying your effort on the bike without a power meter – isn't a bad thing. But the PowerCal isn't a power meter, and shouldn’t be presented as one.
