As long as it has locked on to a minimum of 4 satellites (most see 8 - 12) it is more accurate. all good units (navman, Tomtom & Garmin) use doppler (frequency) shift for speed & time shift for lat/long location & not way points.

lat/long accuracy is irrelevant, the system uses a totally different method to calculate speed over ground.

"GPS receivers typically calculate velocity by measuring the frequency shift (Doppler shift) of the GPS D-band carrier(s).

Velocity measured by a GPS is inherently 3 dimension, but consumer GPS receivers only report 2D (horizontal) speed on their readout. Garmin's specifications quote 0.1mph accuracy but due to signal degredation problems noted above, perhaps 0.5mph accuracy in typical automobile applications would be what you can count on."

.5 mph = 0.804672 kph pretty accurate no?

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