I normally train on my single using a power meter to help judge intensity. Because we were riding a lot more on our tandem this year I installed vector power meter pedals on the front of our tandem.
I have really liked having the power readout because in the past I have pushed too hard at times when trying to ride on the tandem, trying to attain the same speeds as on my single. It has been very interesting noting high power output levels when climbing and during accelerations. The meter allows me to more easily limit my output to sustainable levels.
Mark W