Patent ID: 6856141

Claim:
A method of measuring a predetermined parameter having a known relation to the transit time of movement of an energy wave through a medium, comprising: transmitting from a first location in said medium a cyclically-repeating energy wave; receiving said cyclically-repeating energy wave at a second location in said medium; detecting a predetermined fiducial point in the cyclically-repeating energy wave received at said second location; continuously changing the frequency of transmission of the cyclically-repeating energy wave from said first location to said second location in accordance with the detected fiducial point of each received cyclically-repeating energy wave received at said second location by utilizing each detected fiducial point to trigger the transmission of said energy wave, such that the number of waves received at said second location from said first location is a whole integer; and utilizing the change in frequency to produce a measurement of the transit time of the energy wave from said first location to said second location, and thereby, a measurement of said predetermined parameter.