The law of variation in the signal with relative placement deviation of the two gratings is analysed and proved sufficiently. And a series of the equations about this law is given.

we asked. 'Measuring the relative speed and angles of the balls, the distances to the pocket and final placement of the white ball?'

Method:40dry atlas specimens were used to measure anatomic data relative to screw placement technique with an electronic digital caliper and a goniometer.