derground path of a boring toolUS5798644Feb 20, 1997Aug 25, 1998At&T CorpMethod and apparatus for locating buried conveyances using locating & confirmation signals with an array of sensorsUS5914602May 20, 1998Jun 22, 1999Digital Control, Inc.System including an arrangement for tracking the positional relationship between a boring tool and one or more buried lines and methodUS5963042 *Mar 26, 1998O