… I didn’t read that list bit carefully and was relating it more to the discussion on the other forum where people were trying to determine speedometer error percent, by comparing it with what the GPS said their speed was. Since GPS’s can have their own inaccuracies, it probably isn’t the most exact method of speed calibration.
But even relating it to Odometer. My understanding is, the Garmin Zumo 600 for example, has an accuracy of 10′. From what I understand that to mean is that is there is a circle of confusion of 10′.. more or less a 10′ bubble that the GPS has determined you are somewhere within. Granted you may be up to 10′ ahead of where it thinks you are, or 10′ behind, so it likely averages out over a long ride.
You sound like you have definitely done your homework along your route though and did a lot of double checking and fact checking, but because of that circle of confusion and other factors that can affect GPS accuracy, I think you would have to do that same homework on every route wouldn’t you?
The reason I ask is I have seen similar posts about GPS accuracy where people using them on cars, bikes, motorcycles, and marathons claim they are not always 100% accurate. The consensus, from what I can gather, is about a 2% error. I am not sure how that compares to the average error on most odometers.
I think part of the discussion on accuracy had to do with that circle of confusion and the clock rate of the unit determining how often it takes a reading. Some talk about whether GPS accurately accounts for frequent lane changes and how much those add up over a long trip, etc. I admit, I am not a statistician, and my eyes kind of glazed over after so much of it.