@Rich: as it has been discussed off line - in case the Cable calculation (phase method) depends on the velocity factor and the exact frequency of the phase jump only, the limiting the freq range around the 180deg jump should give you the best result. Theoretically the increasing the velocity fact input precision (like 69.5%) and the printed out number of digits of the length (like 5 instead 4) would give you even better practical resolution then. 73
