My experience has show paddle wheels to be more accurate than the pressure
pickup but they are usually still off by a couple mph.

As to the accuracy of GPS. Look up any specs on the units at garmin.com.
Accuracy:
a.. Position: 15 meters (49 feet) RMS*
* Subject to accuracy degradation to 100m 2DRMS under the United States
Department of Defense-imposed Selective Availability Program.

a.. Velocity: 0.1 knot RMS steady state
Velocity is very accurate as it is a simple time shift of three or more
satallite signals.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"Wayne.B" wrote in message
...
On Mon, 30 Aug 2004 03:44:58 GMT, "dixon"
wrote:
I have wondered if the paddle type is flawed in theory. If you placed the
paddle in uninteruped water, such as say alongside or in front of the
boat
it should be accurate except for water current. I've been suspicious
about
the water the boat is displacing being accelerated along the bottom of
the
hull.
====================================

All of the high quality paddle wheel speed units have a calibration
control where you can compensate for hull effects.