Per Cent Additive : The parts of additive per 100 parts of cement either by volume or by weight. Per cent usually refers to per cent by weight. If per cent by volume is meant, it should be so stated. (Bul 10C)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}