Maybe the info here would help.. George http://www.patentlens.net/patentlens/patents.html?patnums=US_4707454&language=&#tab_1 http://www.ptb-sales.com/manuals/electroglas/1034-option-d.pdf http://origin-www-ca.computer.org/csdl/mags/mi/1981/02/04070671.pdf