Let me just say this before I begin, this post was not intended to compare the merits of a $100 power meter/HR monitor made by Power Tap to that of a $1500 power meter made by Racermater aka Computrainer. There is no comparison. What it's intended to do is show/highlight the PowerCal for what it is. That is, it's an inexpensive tool to get you into the "power meter" world without taking a 2nd mortgage out on your home. Just like you can go to a store and buy a $100 micrometer vs. $1000 micrometer, they both do the same job..measure things. It's just that one does it with better accuracy/precision than the other. Naturally, the higher the price the more accurate. Same applies with power meters.
From the research that I've done, I read/heard the PowerCal power meter/HR monitor has better reliability (closer accuracy) with longer steady-state efforts rather than shorter intervals. So, I set out to see if this was true, and lo and behold- it is/was. Granted, this is not a scientific study and the sample size is not large enough to give it any statistical significance. Nonetheless here it is. See Chart below:
You can see that as the intensity increases (L1 thru L4) the change in watts (delta) between the Computrainer and PowerCal increased. I can only assume that's because of the short 5 minute intervals. So, I decided to do a longer interval at L4 (20 minutes instead of 5 minutes). You can see that the delta decreased from 30 watts to 10 watts. That is, the PowerCal was more accurate at longer steady-state intervals. I tried to maintain the target watts of 225w at L4 but I could only muster 205w. Just not on my A-game since I rode hard on Tuesday night and it's currently Thursday night. Yeah, I know, it's 2 days..but I'm almost 60 and I seem to need 3 days rest before hard workouts rather than 2 of yesteryear.
I'm really happy with my PowerCal power meter/HR monitor for $100. It does what it was intended to do and that is get you in the ballpark of the power meter game. As I said before, it's not intended to compare with the more expensive power meters on the market, but it will get you in the game/ballpark..and that's what I wanted. If I want better accuracy I'll use one of my more expensive power meters on a ride- that has better accuracy.
BTW, I own 2 computrainer power meters at $1500 ea. (one is Lab quality), an iBike Pro power meter at $400, 2 Power Tap power meter hubs at $700 ea. And, now a PowerCal power meter/HR monitor. That's over $4000 worth of power meters. So, it's not that I don't have any other power meters or I can only afford a $100 power meter.
Power ON! Coach Rob