Go-Devil 2 : A term used to describe a tool or instrument that is dropped and free falls from the surface through the drilling fluid within the drill stem. (Bul D20)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}