Limits of motion: the rotating sleep surface is rotatably affixed to the lower fixed base by four screws and washers attached to screw bosses extending upwards from the lower fixed base. The bosses, screws, and washers must not contact the moving platform during normal operation. Arc-shaped slots in the moving platform that the bosses pass through shall allow the moving platform to rotate 3.5° ± 0.2° in either direction (a total of 7.0° ± 0.4°) before interference occurs between the bosses and the ends of the slots. This interference must limit rotational movement before any other interference occurs.