The centrobaric method was used to determine the position with the maximum modulation value of fringes and the position was used as the point of zero light path difference.

采用重心法确定干涉条纹调制度的最大值位置，并以此作为零光程差位置。

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Since the speed of light through a cable is consistent, the difference is entirely in the length of its path.

WSJ: A Dive Into the Digital Deep