Why is power different between Newton and Garmin 810

[Guidob]

I just purchased a Garmin 810 and have set it up to receive power readings from my Newton. For some reason the ride summaries relative to power are substantially different. For example the result of a 1 hour 16 minute ride is:

Avg Power Newton: 252W, Garmin: 228W
NP Newton 301W, Garmin: 280W
IF: Newton 1.07, Garmin: 1.00
TSS: Newton 147, Garmin: 124
60 sec Max power: Newton (from Training Peaks): 604W, Garmin: 535W

Since the Garmin is getting the power data from the Newton, why are they different. I would expect them to be very very close if not exactly the same?

Does anybody have any explanation why the data is so different? The Newton is set to display power smoothed at 2seconds, while the Garmin displays a 3 second smoothed power. However, the filtering should only affect what is on the display, not the post ride analysis. The Garmin is set to include zeroes for power analysis, I don't know if the Newton includes or excludes zeroes.

Does anybody have any explanation why the data analysis is so different? If including or excluding zeroes for power is the reason,why Garmin is lower, what is the proper setting for dealing with zeroes for power analysis?
Thanks,
Guido

[dtrousdale]

I've observed the exact same thing--except in my case, I'm getting a signal from a DFPM to both my Garmin and my Newton--and have asked this question but have not received an answer. The DFPM data is sometimes significantly different when recorded on each of these head units.

I've been advised that with the Garmin, you should choose the option to count the zeroes (from coasting or from stopping for whatever reason) to get an accurate measure of your expended power. The zeroes can represent recovery time, and if you don't count that, you are not getting an accurate picture of the overall effort. I don't know how Newton+ handles coasting, but I would guess it counts only rolling time since the timer stops when you stop.