FUNCTION HAVERSINE
!---------------------------------------------------------------
!*** Haversine Formula - Calculate distances by LAT/LONG
!

!*** LAT/LON of the two locations and Unit of measure are GLOBAL
!*** as they are defined in the main logic of the program, so they
!*** available for use in the Function.
!*** Usage: X=HAVERSINE


    Radius=6378.137
    Lat1=(Lat1*MATH.PI/180)
    Lon1=(Lon1*MATH.PI/180)
    Lat2=(Lat2*MATH.PI/180)
    Lon2=(Lon2*MATH.PI/180)
    DLon=Lon1-Lon2
    ANSWER=ACOS(SIN(Lat1)*SIN(Lat2)+COS(Lat1)*COS(Lat2)*COS(DLon))*Radius

    DISTANCE="kilometers"
    SELECT CASE UNIT
           CASE "M"
                HAVERSINE=ANSWER*0.621371192
                Distance="miles"
           CASE "N"
                HAVERSINE=ANSWER*0.539956803
                Distance="nautical miles"
    END SELECT

END FUNCTION