Decibel (db) 04 : A unit of sound intensity, loudness, or pressure level in which 0.0002 microbar of pressure equals zero db sound-pressure level; the threshold of hearing. (Bul D11)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}