Expanding on the linked posting of 30 Apr 16, just imagine what you could do with - for example - a transient source relative time-difference-fix (TDF) tracking solution of an otherwise undetectable or very marginally detectable target-of-interest that provided an over-the-ground solution of 6.012 nautical miles (mean value: 1,852.3 meters or 6,077.03 ft) in 30 minutes plus/minus two feet). That's an error of one part in 9,134 or 0.11 percent, which may be least as refined as the output of a ship's inertial navigation system.

And you don't even have to know the position of the sensors. You only have to know the sensors did not move during the measurement period.

Other important derivables of equal accuracy are possible but cannot be discussed on this venue.

Bruce:
It is Sunday night, and my attention is being split between The Yankees at Fenway, and your relative TDF discussion. Having a hard time wrapping my mind around the discussion, but love thinking about it. Sunday evening............Yankees/Red Sox........TDF solutions.........I think I'll have another sip of Blanton's...........