Tracking a boring tool is performed within an underground region using a locating signal. The boring tool is moved through the ground during a series of distance movements such that potential movement of the boring tool during any one of the distance movements is less than a maximum movement value. A...http://www.google.co.uk/patents/US6917202?utm_source=gb-gplus-sharePatent US6917202 - Boring tool tracking/guiding system and method with unconstrained target location geometry
