Abstract: A pendulous compensator for use in a light beam projector including a light beam source comprises first and second upper pulleys spaced from one another and secured to the light beam projector. First and second lower pulleys are positioned beneath the first and second upper pulleys and supported by filament strands, tapes, loops or the like extending around the upper and lower pulleys. A pendulum mirror is secured to and supported between the first and second lower pulleys for receiving a light beam from the light beam source and reflecting the light beam in a desired angular orientation relative to horizontal. The first and second lower pulleys in the pendulum mirror are supported such that the pendulum mirror is moved to compensate for tilting of the light beam projector. The first and second upper pulleys or a folding mirror may be controlled to select a grade angle relative to horizontal of a projected light beam.

Abstract: An apparatus and method are provided for measuring the included angle of a reflective cone between opposite sides of the reflective cone. The apparatus includes means for illuminating the curved surface of the reflective cone with a collimated beam of light, the beam of light being generally parallel to the axis of the cone. A lens receives directly a portion of the light reflected from a first side of the cone, and focuses the portion of the light so received in a reference plane. A retro-reflective mirror arrangement, positioned on the side of the cone opposite the lens, receives directly a portion of the light reflected from a second side of the cone and redirects the light to the lens in a direction parallel to the light reflected from the second side of the cone. The second side of the cone is opposite to the first side of the cone.