The OHD FitTester 3000 Controlled Negative Pressure (CNP) is easy to operate, can be set up in minutes and requires no certification. A one-minute daily calibration verifies the instrument’s accuracy and integrity. The portable unit uses air as a test medium, which allows testing to take place in any environment. The FitTester 3000 is calibrated to NIST traceable standards.Occupational Health Dynamics, Birmingham, AL.