DR wrote:

On my 12 channel boat GPS I see a
HDOP of ~1m these days.

HDOP is unitless.

Good point. I'm sorry that I was being so loose. But you could descibe
the 1 sigma dilutuion of precision in terms of distance at your position
and time -right? I was actually amazed to see that my Ryatheon GPS put
my boat right in the center of the correct dock -implying 2m accuracy
(or better)!

Cheers MC

I have to think about it. Position accuracy is given by this generic
equation:

DOP x UERE x 2 = position accuracy (2 sigma or 95%) where UERE is the
combination of the space and user equipment error sources.

Ron Lee