I searched the forums and found scant discussion on measurement of power for tandems. Being the quintessential quantoid (Sorry, I couldn't resist the alliteration), I never seem to have enough performance data. Well, there is a new device IBike Pro power meter http://www.ibikesports.com/
(I have no stock or any interest in the success of this company.) that measures power indirectly instead of using a hub or other device and provides massive amounts of data – power, speed, elevation, wind speed and etc. The device can be used on several bikes (one meter with several mounts) including a tandem. I called the company and talked with them about tandems. According to the company there is no problem using it on a tandem once one completes the calibration procedure. All data from the power meter is downloaded to a PC or Mac and there is lots of data manipulation and graphics!
It is clear why one measures power on a road bike. Power is the best way to train and supposedly superior to heart rate. It is less clear if power on a tandem is worth the money, USD 400. There are a number of threads discussing the IBike Pro in road cycling. The biggest negative is that drafting can corrupt the power measurement due to disturbed air from the cyclist in front and there is the calibration. Otherwise, it seems to get reasonbly good reviews. The hub is the best way to measure power (expensive) but it is not practicle for tandems.
Let us assume for the sake of argument it works, what about tandems???? I say fantastic. The more objective we are in the way we measure performance the better the team trains and performs – and hence more fun. What do you think?