Captain Will, Interesting formula. Don't the minutes and seconds have to be converted to decimals of a degree prior to calculating? Regards, Sandy and Dawna Floe M/V Sea Eagle Puget Sound . 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) >