The accompanying photos and drawings illustrate this. Fig 6. . At one end is the light source and knife edge while the mirror holder can slide along the full length of the rail. The Minor Holder. The mirrors are held in a ring with trunions that fit into a fork on the slide.
Mirrors locate on the front face against nylon washers and are held by two nylon fittings.
The rings are lifted out of the fork onto the bench to fit the mirrors. Once their initial adjustments have been made to return the slit image back to the knife egde, mirrors can be removed and replaced without any further adjustment. Control cables run the length of the rail to tilt the mirror up or down and left or right. Handwheels are within reach of the observing position to make the adjustments. When positioned the mirror holder can be locked in position.