Originally Posted by j814wong

I just found an app of Google Play that claims to "without calibration (only entering rider's weight and choosing bicycle type), average power for a given ride typically correlates to within 15% (with no drafting) of a conventional power meter." Of course, my first reaction was "Wait... WHAT?!" After all, normal powermeters are so damn expensive because of all the fancy secret technologies tucked inside them or maybe they are also just overpriced because companies know cyclists would pay good money for such things. But in any case, a $8 power meter app is intriguing and while serious cyclists won't care for the app because of the +_15% difference in accuracy to normal power meters, I think that the concept could be a good replacement for those of us who don't have the money for a $1000 power meter.

The reviews for the app are quite good (Average 4.9 stars). I don't have a power meter myself so I can't compare the accuracy of the measurements. But to be honest, I a bit suspicious.

Oh, it also can estimate cadence and % braking energy. Yeah, color me skeptical but when the weather lets up in my area, I'll give it a go and compare the cadence measurements to that of my Garmin.

Quoting their FAQ on cadence...
"How is the app able to detect cadence without a cadence sensor?
The phone's low power accelerometers along with advanced signal processing techniques are used to detect the small acceleration differences seen due to normal rider's output power variation through the crankshaft cycle. Figure 5.7 in the book High Tech Cycling by Ed Burke illustrates this effect. The effect is more challenging to detect for mountain bike riders (more constant power vs. angle and more vibration noise). Wearing in a jersey pocket has produced the best (lowest noise) cadence results, but a handlebar mount can also work reasonably well. Noise and errors are common when the power to weight ratio drops (i.e. coasting or soft-pedaling) since accelerations can be dominated by other effects in this case."

Thoughts?

Note: Google Play has a crappy 15 minute return policy on paid apps (It ought to be at least 30 minutes in my opinion).