You might have better luck. I suggest ordering three gauges and three calibrators. If they all match, you're good. So far I have two defective sound pressure level meters. It was one of them. I also bought a calibrator which is equally inaccurate at all three meters. Let's see if the following two calibrators agree.
π Enhanced Precision with Backlit Professional Manometer for Differential Ventilation
6 Review
π¬οΈ Advanced 3-in-1 Indoor Air Quality Monitor with CO2/RH/Temp Data Logging and Audible Alarm - NDIR Sensor Technology
8 Review
π Dioxide Controller for Digital Gas Monitoring
5 Review
π₯ Advanced Testo Wireless Hot Wire Anemometer Technology
4 Review