A = LAT1, B = LONG1
C = LAT2, D = LONG2 (all converted to radians: degree/57.29577951)
IF A = C AND B = D THEN DISTANCE = 0;
ELSE
IF [SIN(A)SIN(C)+COS(A)COS(C)COS(B-D)] > 1 THEN DISTANCE = 3963.1*ARCOS[1];
ELSE
DISTANCE=3963.1*ARCOS[SIN(A)SIN(C)+COS(A)COS(C)COS(B-D)];