The datum of four-jaw correction is usually the end face of the workpiece and two mutually perpendicular center lines (a parallel guide rail and a vertical guide rail), AB and CD, commonly known as crosshairs. There are three ways to correct the reticle: 1. Put the crosshairs in front of the guide rail and correct the crosshairs on the back two faces; 2. Fix the crosshair on the middle support plate, and shake the middle support plate (with large support plate) to correct the crosshair of the workpiece; 3. Workpiece requirements. Correction of shaking tray or large tray