If you change to UTM instead of LAT/LON you may notice an apparent higher degree of accuracy. This is because UTM is based on a 1000M (1KM) grid system. Unfortunately if you are using nautical charts, this may not be real convenient, but since I am using USGS maps about 99.7% of the time, I use and prefer the UTM system.

Don't have my GPS here with me (at work), but there are at least 4 decimals in a UTM coordinate (5 I think, but do not shoot me if I'm wrong ). 4 places would be at a 1 meter level.

: Perhaps you wanted to be an early innovator?

: The differential add-on uses, I believe, LORAN signals and calculates a
: position from that, as well as from the GPs. The combination of the two
: should be more accurate than either alone. Should the government ever turn
: that GPS "selective availability" error back on -- say in case
: of war -- you'll be better than most of us.

: My GPS displays a position down to hundredths of a minute. (degrees, minutes,
: and 00 to 99/100ths of a minute) Assuming the signals and the calculatons
: in my receiver are accurate, that should get me somewhere within a 60 foot
: circle of my actual position. As I see it, I would need three decimal
: places (thousandths of a minute) to get *a display* of accuracy within 6
: feet.

: Now this just applies to the actual indicated position. I suspect that when
: my GPS calculates my my position it really knows the answer to more
: decimal places than are displayed on the screen -- and it uses these more
: precise figures to calculate such things as velocity. Otherwise, how would
: it know I had moved if I was going at only 2 miles an hour? Hopefully the
: change will give me more accurate speed readings, but until I get a GPS
: that displays another decimal place, I can't see how I will be able to
: determine my position any more accurately than before. Maybe I'll just be
: more certain that what I am seeing is really right.

: PGJ