Having done two days of riding in hillier country than I usually ride I was taken back by the power numbers the Newton was reporting in real time, and which I saw in Isaac afterwards (and after an Analyze Route, which is obligatory to get the start and end elevations correct and to remove the headwind bias from almost every ride, even though I do a Wind Cal before each). When back home the next day I did a ride with a Ptap wheel and I marked, with laps, a number of sections to analyze later (after the Analyze Route). I used the power and speed calculator at https://www.gribble.org/cycling/power_v_speed.html and input the same CDA, Crr. weight, and CM as in the Newton then input the speed, slope and wind from the Newton for each of the 4 sections. The four sections were: two flat, one aiming to hold 200 watts (2.5 minutes), the other 300 watts (3.5m); one uphill at 7% grade (1m) and one slightly downhill at -.9% grade (5m).

I compared the Newton and Ptap average power over those sections to what the equations of motion said the average power should be, using both speed vs ground and speed vs wind as reported by the Newton. I should say that my bike speed is correctly dialed in, I've done 100+ mile rides with this setup and the Newton odometer has been off by only a few 10ths of a mile from the ridewithgps mileage. The results were (using speed vs wind):

_____________Newton____Ptap___Eq of Mot.

200W section:....243.........206......205

300W sect:........307.........299......292

Uphill 7.1%:.......288.........233......233

Downhill .91%:....160........132.......140

Over the total of 12 minutes, by time weighting the 4 sections, the Newton was on average 25 watts high vs the calculated value, and the Ptap was 1 watt low.

I had thought the ongoing problem of the Newton consistently reporting watts that were too high was a problem with its wind or slope sensing, but it looks now like those are accurate (confirmed by the Ptap), and the endemic problem is that it can't do the equations correctly. What do you think?

Ride file attached, the laps in question are 2, 4, 8, and 10 in the lap list.