A number of laser beam stations emit vertically separated parallel planes and/or ray-planes of laser light that can be discriminated by their respective plane elevations, modulation of the laser light, time synchronizing, etc. Identifying the laser plane would also imply an identification of the source laser beam station, and thus a precise indication of the elevation at the point of optical intercept. Alternatively, a single laser beam station is used that can emit several different monochromatic color planes and/or ray-planes of laser light. Monochromatic laser diodes, for example, are used for point-light sources and rotating or on-end conical mirrors are used to convert the diode laser light to the required monochromatic color planes and/or ray-planes of laser light. Receivers, generally held on masts attached to motor grader, bulldozer, loader, and excavator machines are used to sense the vertical reference position of the monochromatic color planes and/or ray-planes of laser light, relative to the earth cutting blade of the machine. Fixed-color filters, color filter wheels, and/or linear array photodetectors are used to discriminate amongst the colors and to exactly sense the plane of intersection with the machine. The results of the sensing are either displayed to an equipment operator for manual adjustment of the blade to an automatic servo control system connected to hydraulically control the blade.