Originally Posted by Bontrager
The HAC4 calculates power like the poster above said. I have the HAC4.
I believe the Polar unit actually measures power by measuring strain or something on the chain.
There's other products that will measure power directly/better. It all matters how much you want to know and spend.
I believe you are correct. I actually read a report that compared the different systems that measure power. At the top of the list was the PowerTaps being the most accurate, with the Polar unit slightly behind the PowerTaps. What they didn't like about the Polar unit was that the power reader is a bit difficult to work with because it seems to slide off the chain or around the chain at times.
Both units are pretty expensive, although the PowerTaps is far more expensive than the Polar.
Koffee