A rotary laser level is affixed to a tripod, leveled and then spun to illuminate a horizontal plane. The laser beam projector employs a rotating head with a mirror for sweeping the laser beam about a vertical axis. If the mirror is not self-leveling, it is provided with visually readable level vials and manually adjustable screws for orienting the projector. A staff carried by the operator is usually equipped with a movable sensor, which can detect the laser beam and gives a signal when the sensor is in line with the beam. The position of the sensor on the staff allows comparison of elevations between different points on the terrain.