Hey Adam,
this is not the first time that I see someone trying to measure a dust collector’s air flow and/or trying to compare dust collection systems with an anemometer. But this is not the right tool for that. Neither it measures the air flow and pressure inside the system (it only measures the so-called ‘short-circuit’ air flow at the open end of a hose), nor is it free of being an obstacle itself, therefore falsifying the result.
What you would need, is a → pitot tube.
In industry, the flow velocities being measured are often those flowing in ducts and tubing where measurements by an anemometer would be difficult to obtain. In these kinds of measurements, the most practical instrument to use is the pitot tube. The pitot tube can be inserted through a small hole in the duct with the pitot connected to a U-tube water gauge or some other differential pressure gauge for determining the flow velocity inside the ducted wind tunnel. One use of this technique is to determine the volume of air that is being delivered to a conditioned space.
Source: Pitot tube – Wikipedia
Image: A pitot tube. Its use is demonstrated by this friendly gentleman.
Video: Measuring Dust Collection Airflow – Woodworkers Journal
Really like your 3D printing projects!