A method of digital phase calibration is disclosed. The objects can be machinery, valves, containers, or any other object whose displacement is to be measured. The pointer may be progressively illuminated by plural light sources disposed behind a scale plate by tuning on the light sources one by one. An active seals are disposed around the conductors and the inner walls of the shell that define the openings in which the shells are seated. By a Fourier transformation, Fourier coefficients are determined as a resultant {right arrow over } at least of the harmonic of the 0.