Originally Posted by babyboomer

I have a Stages power meter which, since the beginning of the year, I've been using in conjunction with TrainerRoad's virtual training application for Windows. Another TrainerRoad user who had occasion to review my ride file thought that the power data it contained didn't quite add up. Initially, I didn't think much of it. After taking a second look, however, I began to suspect that he might have a point.

TrainerRoad's virtual training application includes a feature called VirtualPower. This feature uses speed data along with the power curve provided by the stationary trainer's manufacturer to calculate power. It is a feature designed to accommodate those using the application without an actual power meter. On those occasions when I used that feature, I noticed that TrainerRoad's VirtualPower calculator was reporting higher numbers for the same perceived effort. So, I conducted a little test. I paired the Stages power meter with my Garmin Edge 1000 cycle computer, and enabled the VirtualPower facility in the TrainerRoad application – the objective being to record power data from both sources simultaneously. During the indoor workouts that followed, I noticed that there was a significant discrepancy between the power reported from each source. Specifically, the power output captured from the stages power meter on the Garmin head unit was 40 to 70 watts lower than that reported by the TrainerRoad application! Additionally, I could not detect a pattern. There was no evidence that the discrepancy changed in a predictable way – for example, increasing or decreasing with the level of effort. A few watts I could ignore, but a difference of 40 to 70 watts is significant! I suspect that the power meter is defective. I was just wondering whether anyone else has had a similar experience with their Stages power meter.