Distances cited are great-circle distances on the earth, with correction for the fact that the earth is slightly non-spherical.
Default is currently the WGS84/NAD83 datum. Latitude and longitude can be entered by degrees and minutes in the separate boxes provided, or as decimal degrees by entering a number like "39.999535" in the degrees box and leaving the minutes and seconds boxes empty.) Minutes or seconds can also contain decimal points.
Default is currently the WGS84/NAD83 datum.