Alignment Optical Telescope diagram. The remaining three detent positions reverse the prism on top of the telescope. The reticle pattern within the eyepiece optics consists of crosshairs and a pair of Archimedes spirals. The horizontal crosshair, an auxiliary line designated the X-line, is perpendicular to the orientation line. Ten miniature red lamps mounted around the reticle prevent false star indications caused by imperfections in the reticle and illuminate the reticle pattern.
Heaters prevent fogging of the mirror due to moisture and low temperatures during the mission.
Alignment Optical Telescope - Detents and Field of View. A reticle control enables manual rotation of the reticle for use in lunar surface alignments. A counter on the left side of the unit, provides angular readout of the reticle rotation. The maximum reading is 359.88 degrees, then the Counter returns to 0 degrees . Interpolation is possible to within 0.01 degrees.