Closing Ratio 1 : The ratio between the pressure in the hole and the operating-piston pressure needed to close the rams on a given BOP design against a particular well head pressure
George E. King Engineering, 5000 Oilfield Terms: A Glossary of Petroleum Engineering Terms, Abbreviations and Acronyms, US 2010. http://gekengineering.com/Downloads/Free_Downloads /Glossary_of_Petroleum_Engineering_Terms_25_August _2010.pdf, (Oil - Amer) {593}