A dimensionless number expressed as the ratio of the actual to the theoretical flow rate of a fluid discharging through an opening or restriction. The coefficient is used as an indication of the recovery of energy following through the opening or restriction. Where there is full recovery and no permanent energy loss, the coefficient is equal to 1. For example, for a well-designed venturi meter the coefficient may be in the order of 0.95 to 0.98 signifying very good energy recovery, whereas an orifice plate meter may be as low as 0.6 at high flow rates. Orifice plate meters, however, are popular since they are considerably cheaper than venturi meters to fabricate and install.