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post #2 of Old 08-12-2019
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Re: GPS determined speed


GPS speed (and course) is based on a few things:
-How often the gps receiver updates (some old unit only receive 1 update per second (1 HZ), newer units can receive 10 updates / second)
-How much filtering is done (both horizontal and vertical)
-How often the display is updated.

GPS speed is your HISTORICAL speed - is how quickly you got to your CURRENT position from your PAST position. I don't believe any gps is accurate enough to provide .1 kt difference AT THIS EXACT MOMENT.

Really .1kt difference is the same speed. At any given time the speed reported by my B&G Vulcan, Garmin GPSMAP 76, and Iphone running Navionics will be slightly different. It's no big deal.


Barry Lenoble
Deep Blue C, 2002 C&C 110
Mt. Sinai, NY

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