RapDaddyo said:
Overboard? What do we use a PM for? To manage intensity of efforts and the most important efforts are our high-intensity efforts. I am suggesting that a rider attempt the same interval on the same course, managing power with the PT or SRM one time and the iBike unit the second time. We use PMs differently to manage power, with different accuracy. A direct comparison of how well the rider achieved his objective with a PT or SRM and with the iBike unit would be meaningful to me. This isn't a long or complicated set of tests. It's a typical workout, simply using first one device then the other to manage an effort. How is that overboard?
And I have no doubt that any of the PMs out there will allow you to do that. Perhaps you should be specific about your concerns. Is it L5, L6, L7? I'd wager that L5 isn't an issue - the intervals are long enough and efforts smooth enough to properly modulate your efforts. L7? Those are all out anyway and over before you can really digest what's on the display. That leaves L6. I tend to use PE for those with power as a guide to keep me honest (no problem overshooting, it's the maintaining L6 that is harder for me).
If you really want to know if the rider achived his objective, it sounds like you're using the wrong PM anyway. We all seem to agree that NP is an effective tool, and only one PM has that functionality on the fly. Everything else is AP and we can only estimate what NP may have been for the work interval.
If you are worried about 2 PMs giving you different values such that one day you ride with a PT and the next an ibike and you worry if you are meeting your goals, well, that's a real problem. But anyone who has more than one brand of PM already deals with that. I've got a couple of PTs, a couple of older ergomos, and a CT. One of the ergomos is way out of calibration, and the CT reads 10-11% low compared to the PT. It's the responsibility of the rider to know his equipment, how well calibrated it is, and adjust the "human filter" when riding those different pieces of hardware. For example, I know that when I hop on one TT bike with my oldest ergomo that I need to see numbers that are 25% or so higher than when I ride with a PT.
Accuracy is one thing, and it certainly is desirable to have. However, the more important quantity is consistency. As long as you have that, you can train effectively no matter if the response of power meter #2 is linear or nonlinear compared to power meter #1.