Height of Derrick and Mast Without Guy Lines : The minimum clear vertical distance from the top of the working floor to the bottom of the corner block support beams. (Spec 4F).
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}