Drop-Type Survey : A directional or inclination survey taken with an instrument that is free released to fall within the drill stem to the desired position within the wellbore. (Bul D20)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}