I think you can scan a paper chart or topo map and then upload to some nav
programs. If you do this you have to calibrate the map by telling the
software what L/L is represented by points selected on the chart. I don't
think the original poster is likely to be doing this.
I'm not aware of any calibration being necessary if you up load commercially
produced charts. I believe the calibration data is part of the chart data.

"William Andersen" wrote in message
news:LhUIf.81$xH.38@dukeread03...
Huh?
"Dennis Pogson" wrote in message
news
Len Krauss wrote:
Having a little problem with my chart display showing my position
approx 150 ft west of actual, I checked chart datum (NOAA BSB raster
type) and found it was NAD83, whereas my GPS (non-WAAS) had been set
to WGS84. So just for the heck of it I set the GPS to NAD83. That
didn't correct the position error. From what I understand, WGS84 and
NAD83 are practically identical, so is there any reason not to just
leave GPS set to WGS84 (this is in SW Florida, USA)?

Any advice on what else to check to correct the westerly error would
be appreciated. (using Capn nav software and Garmin GPS 48).

Thanks,
Len

It's your calibration data that is off by 150ft. Re-calibrate (if your
program allows it!)