The Autocollimator is used to fine tune the optical alignment after using the LightPipe/SightTube or a laser collimator. It utilizes a flat mirror that shows multiple reflections through the optical system. This is 2-4 times the accuracy of a Cheshire, LightPipe or laser collimator. The adjustment screws are then locked to insure lifetime accuracy. Includes a 14 page instruction booklet.