The type of impeller fan motors used in the Bio-Pump are easily affected by backpressure. Backpressure is created by small orifices (even 1/4" openings), tubing and the length of tubing used. Since most standard calibrators either use 1/4" fittings or require power to move a piston, the backpressure they create on the pump is not representative of actual use and this alters the flow reading. Zefon has designed the Bio-Pump flow meters to simulate the exact backpressure the pump is subjected to during use with a cassette inline. Because of this unique design, this flow meter cannot be used with any other pump. Verification of the flow indicators provided with the Bio-Pump may be performed using a TSI 4046 Primary Flow Calibrator, which is considered a primary standard and is available with NIST certification.