Is trip meter accurate on GPS

[jworks]

I have an old Magellan GPS 315. I know its old, but I got it basically just to tell how far to my take-out point on a kayaking river trip.

Here's the question: Google Earth tells me its 3.25 miles between put-in and take-out places. Yesterday the trip meter on my gps said I'd traveled only 2.4 miles. Thats a big difference, 27%. The river is surrounded by woods, steep bank and high hills. Its not uncommon for a gps to lose signal in this country and pick it back up several times. QUESTION: If the gps lost signal several times and picked it back up will the trip meter calculate for the time offline and fit that in to the mileage? Or, does it just pick up where it left off and calculate from the new signal contact point? Today I measured it against my car trip meter and it is the same as the car meter. So, that leaves me wondering if mileage distance on Google Earth is inaccurate or could my Question above be what's causing the difference? In other words, can Google Earth mileage be trusted or is it off?

 

[Nuvi-Nebie]

If the GPS looses signal the only thing it can do is to draw a straight line between the last good position and the point where it re-gains it's position, this will mean that you get a series of curved 'actual' readings joined by straight lines, the total distance will be reduced because the real path will always be longer than the straight lines


Measurements in Google Earth can also be inaccurate because you are choosing where to put the sample points and the number of them, also you may be using old data and the river shape has changed since to picture was taken

 

[Ceve]

10/10 answer.