How is fringe displacement calculated?

Человек открывает коробку с логотипом Beckman Coulter
The system performs a single-point discrete Fourier transform (DFT) at the frequency represented by the fringe vertical frequency. This transform is calculated on each vertical column of data, across the entire row. The phase of each calculation is used to calculate fringe displacement (1 fringe displacement = 360 degrees of phase shift).