1. ASHTECH XII GPS receiver;ASHTECH,1990
2. Challenger 65B agricultural tractor;Caterpillar,1990
3. Navigational tractor guidance system;Choi;Trans. ASAE,1990
4. Microprocessor controlled technology to selectively spot spray weeds;Felton,1991
5. A control system for off-highway vehicles;Larsen,1968