I finally sprung for a bike computer with wattage in addition to cadence and heart rate. It's a Polar S-720i and I've finally gotten it to work. Here are some tips and what I've learned so far about training with wattage:
h4. Tips on using the Polar S-720i
After you follow the directions carefully, but it is a little flaky otherwise:
# "Sandiway Fong on S-710i installation":http://external.nj.nec.com/homepages/sandiway/bike/feather/tt/s710/index.html. This applies to the S-720i too. Wish I had read this before I installed it.
# "Checking Polar installation":http://mywebpage.netscape.com/rechung/wattage/testing/testprotocol.html. Here's how to test the Polar to make sure installation is accurate. The main issue is that the chain speed sensor at the derailleur picks up interference. Main idea is move the chain speed sensor as close as possible to the chain. You also want the chain tension sensor as high as possible. It should actually hit the chain on the small-small gear combination.
# Ever so often the thing will go to zero across speed, cadence and wattage and beep twice. What has happened is that the watch is loose, there are two contacts on the back that have to be hard up against the bike mount. Jiggle the watch and it will slip in, beep twice and you are back in. I've found this happens no matter how tight the band is.
# When you start, you _must_ follow the watch to record correctly: a) wet the heart rate monitor belt thingy, b) push the red start button on the watch and you must _wait_ until you see a heart rate reading at the lower left (otherwise, heart rate won't get recorded), c) push on the upper right button until you see the Trip odometer, d) hold the upper left button for 5 seconds to reset the trip meter otherwise, the distance won't be right.
h4. Chris Carmichael on Power used in training
Why use Power Meters. Watching your wattage during the course of a ride is not very useful. Wattage fluctuates quickly and often; heartrate is a much better gauge of workload during a workout.