High accuracy mass flow verifier with multiple inlets

A high accuracy mass flow verifier (HAMFV) which provides high measurement accuracy over a wide flow verification range with low inlet pressures is disclosed for verifying flow measurement by a fluid delivery device. The HAMFV includes a chamber defining a plurality N of inlets with upstream valves, an outlet with a downstream valve, a pressure sensor and a temperature sensor configured to measure the pressure and the temperature of the fluid within the chamber, respectively. A plurality N of critical flow nozzles is located adjacent to the corresponding upstream valve. The HAMFV further includes a controller configured to activate one of the plurality N of critical flow nozzles based on the desired flow verification range and the fluid type by opening the corresponding upstream valve and closing all other upstream valves. At least two of the plurality N of critical flow nozzles have different cross-sectional areas.