1. A method for deriving from pulses at a known pulse rate a continuous logical output in a preselected base, functionally related to pulses at an unknown pulse rate, comprising the steps of: generating pulses at an output pulse rate functionally related to a difference between said pulses at an unknown pulse rate and a multiple of said pulses at a first known pulse rate; generating an output functionally related to said difference; generating pulses at a second known pulse rate having a predetermined relationship to said pulses at a first known pulse rate; repeating the above steps to obtain a plurality of said outputs functionally related to said unknown pulse rate to a preselected precision of measurement, wherein said pulses at an output pulse rate become the next said pulses at an unknown pulse rate, and said pulses at a second known pulse rate become said pulses at a first known pulse rate.