An apparatus for visibly indicating a spatial plane is disclosed, including a light emitter for generating a beam of light, means for dividing said beam of light into a pair of light beams, and means for scanning that pair of light beams in a pair of planes, wherein the planes in which the light beams are scanned are adjacent, symmetrical, and on either side of the spatial plane which is to be indicated. Specifically, the light emitter is a laser, and the means for scanning the pair of light beams includes penta-prisms which are rotated for scanning purposes. Preferably, the light beams which are scanned include high and low tensity areas, and the low tensity areas overlap in the spatial plane to be indicated.