Patents.
4,676,792; 4,682,024; 4,682,025; 4,687,281; 4,688,941; 4,695,123; 4,696,551; 4,696,569; 4,697,577; 4,699,474; 4,699,476; 4,699,477; 4,702,568; 4,702,569; 4,704,008; 4,704,009; 4,704,010; 4,704,011.