A system for providing measurements while drilling a well in which a drill string, made up of standard lengths of drill pipes, some of which may be drill collars, extends from the earth's surface in a borehole, drilling fluid being circulated in the drill string and borehole, the measurements being transmitted...http://www.google.com.au/patents/US4520468?utm_source=gb-gplus-sharePatent US4520468 - Borehole measurement while drilling systems and methods
