Average Power strangeness

[KenS]

I went for a ride today aiming to average 200W. I had the Newton and Garmin 705 running with the Garmin recording the power from the Newton. As I got a few clicks from home I checked the Garmin and it said my average was 198W. So I upped the effort a bit and next time I looked I was at 200W. I then checked NP on the Newton and it said 199W. Strange, I thought, how can NP be less than average? Anyway I put in a bit more effort to get over 200W NP for a bit of fun. Next set of lights I checked the Garmin and it says 201W average and the Newton has 198W NP! Another push and at the next reading the Garmin says 202W and the Newton now has 197W NP. I backed off so as not to wipe out my days effort before I got home
Once home I downloaded both the ride file and the Garmin TCX. The ride file says my average power was only 157W. Now in the past I've had very good correspondence between the Garmin and iBike so why the big difference? Looking into the TCX file it looks like it power never goes to zero although it does display zero. My guess is that it displays zero when the Newton isn't transmitting. So maybe a function of the fact I don't use 1 sec recording in the Garmin whilst I do on the Newton.
Ride file and TCX attached

16_10_2012_1541_iBike.ibr

Ride File

(176.06 KiB) Downloaded 313 times

16_10_2012 3_41_34 PM_history.tcx

Garmin TCX

(553.96 KiB) Downloaded 474 times

[KenS]

I did a little more investigating. It turns out the Garmin never records (or maybe never receives) zero power readings - even with the Gen3.
But both the Gen3 and Newton previously it used to drop down to a few watts whereas since OS2 came in the minimum power is almost never less than 20 watts and often 30 or so. So the nett result is a significant increase in average power recorded on the Garmin.
Attaching a ride file and Garmin TCX from before OS2

03_10_2012_1508_iBike.ibr

Ride file before OS2

(267.96 KiB) Downloaded 312 times

3_10_2012 3_08_14 PM_history.tcx

Garmin TCX before OS2

(745.94 KiB) Downloaded 397 times

[Velocomp]

I looked at your ride files.

Your Newton is calibrated properly and is doing just what it should: zero power whenever cadence is zero.

Your Newton transmits power data roughly four times per second. Data is transmitted continuously, even when power is zero.

I am not familiar with Garmin's recording techniques, but I believe they do some things a bit peculiarly. We are confident our numbers are correct.

[lorduintah]

Many of the Gamin's will let you use zero power as input for averaging or NOT. (User's choice in setting one up.)

tom