Distance1: Miles
Distance2: Miles
Frequency: MHz
100% of F.C.Z.: ft across to radius
  60% of F.C.Z.: ft across to radius

D1 = Distance from site1 to calculation point
D2 = Distance from site2 to calculation point

Note: When calculating F.C.Z. from site1 to site2
          you have to consider D1=D/2 and D2=D/2