 Norman B. Spedding, however, registered a patent in 1994 with several examples showing that it was possible.Although it is not possible to distinguish 2"n" positions with "n" sensors on a single track, it "is" possible to distinguish close to that many.Etzion and Paterson conjecture that when "n" is itself a power of 2, "n" sensors can distinguish at most 2"n" − 2"n" positions and that for prime "n" the limit is 2"n" − 2 positions.