Tester Quality and Calibration: Cheap AC noise testers from China are not accurately calibrated or sensitive enough to detect the specific types of noise reduction that the AC iPurifier targets. These testers measure in a very narrow band and have limitations in their measurement capabilities. Measurement Methodology: The method used by the tester to measure noise does not align with the way the AC iPurifier reduces noise. The AC iPurifier employs Active Noise Cancellation (ANC) technology, which is not properly captured or reflected by simpler noise testers. Interference from the Device: The testers pick up on electromagnetic interference (EMI) or other forms of electronic noise generated by the itself during its operation. False Positives/Negatives: Inexpensive testers might produce false positives or negatives due to their limited accuracy. They may show an increase in noise due to factors unrelated to the actual performance of the AC iPurifier.