>I'm working on a spreadsheet to get a paper copy of all the waypoints >entered in my loran, along with calculated course, distance and time >information as a backup to the loran. In order to do that, I need to >convert the difference in lat/lon bedtween two locations (waypoints) >into nautical miles. The Naval Institute Press published a very ueful book, "The Calculator Afloat" which has all the formula. There are different formula for different types of calculations. The one below is for Great Circle distances. D : Distance between locations L1 : Latitude of departure L2 :Latitude of destination Lo1 : Longitude of departure Lo2 : Longitude of destination DLo : Difference in longitude in departure and destination C : Initial Heading cos D = sin L1 * sin L2 + cos L1 * cos L2 * cos DLo cos C = (sin L2 - cos D * sin L1) / (sin D * cos L1) tan C = (sin DLo) / (cos L1 * tan L2 - sin L1 * cos DLo) The symbol * means times. Good Luck CaptnWil 40 Pier Pointe New Bern NC 28562 (252) 636-3601 captnwil@coastalnet.com