This is just a brief update to the long term review of the Polar CS600X. In fact, the chain tension based W.I.N.D. Power Sensor has I think been discontinued now that Polar pedal based power system has been released. Since buying a Garmin Edge 500, I don't use the Polar out there on the road. This is principally because it's so fiddly to get the thing reliably working with the GPS and power units. So it's been mostly used on the turbo trainer (without the GPS, obviously).

I've been having a bit of trouble with the power unit lately, and I thought I'd add an update.

The reason that the power unit is complicated to set up and keep working is that there are three components:

1. The main sensor/transmitter. This picks up vibration in the chain, so needs to be the correct distance from the chain, but also positioned correctly on the chainstay. This requires judicious positioning in 3D for it to work consistently. The second function is to collect cadence data from the magnet on the crank arm. So the position of the sensor on the chainstay needs to take proximity to the crank arm magnet into consideration. If either of these don't work, no data is sent to the head unit, with no indication where the problem lies.

2. The chain speed sensor. This is mounted on the rear derailleur, and the instructions aren't terribly clear on its exact positioning. As I discovered yesterday, if it isn't just right, no chain speed data are obtained. If it's incorrectly positioned, the system may work in some gears only. The chain speed sensor is connected to the main sensor by wire - this connection can fail. If this doesn't work, no data is sent to the head unit, with no indication where the problem lies.

3. The battery pack. Batteries can wear down, and the connection with the main sensor can fail.  If this doesn't work, no data is sent to the head unit, with no indication where the problem lies.

So, you can see that there are several points of failure, with no real diagnostics in place. If any point fails, the main symptom is that no power or cadence is displayed. This is the main reason I'm dissatisfied with the system. I'd think about this with any power meter system in the future. For the time being, I seem to be able to get along with the system and I'm not inclined to change just now - though the cleat based system from Brim Brothers looks interesting (but may ultimately never be released).