When first using the Testo 510i with the Smart Probes app, you need to zero the pressure sensor to make sure your readings are accurate. Whenever we use static pressure probes, we want to point the tips in the direction of the airflow.

Bryan takes one probe and puts it in the filter door to measure the return static (with the probe pointing down). He also places the positive probe into the supply duct. The Testo Smart Probes app display shows use that the total external static pressure is 0.34″wc (inches of water column), meaning that we are within the specifications for the system’s rating of 0.5″wc.

Testo: https://www.testo.com/en/