Among the three Spectra Precision Laser transmitters is the model LL600, which provides a reliable elevation reference with a diameter range of 2,600 feet. It also features a manual slope mode. The transmitter works with a model HR500 receiver for general construction, and with a CR600 receiver for machine control. The HV601 and HV602 are high-precision horizontal/vertical rotating lasers for general construction and interior applications. They are self-leveling and have a remote control.