This product or its systems are covered by one or more of the following U.S. patents: 4,906,853; 5,017,794; 5,027,314; 5,119,104; 5,276,496; 5,548,637; 5,572,195; 5,355,222; 5,387,993; 6,104,295; 6,154,139; 6,838,992.