Hi, My cave survey freeware connects to a GPS for surface tracking. When I connect to a Bluetooth GPS, the GGA and GSA NMEA sentences provide various flavors of DOP values (PDOP, HDOP, VDOP). How can I provide users with a rough error value in meters (as most GPS units do) from these unitless numbers? Luc Le Blanc [URL]http://www.speleo.qc.ca/Auriga[/URL]