Anemometer
An instrument that measures air speed. Hot-wire types resolve the low velocities inside a canopy; vane types stall before reaching them and read zero in a room that is moving air correctly.
Two types turn up in a grow room. A vane anemometer spins a small propeller and needs a real push to turn, so it typically stalls somewhere around 0.3 to 0.5 m/s. A hot-wire anemometer measures how quickly a heated element loses heat to passing air, which stays sensitive down to almost nothing.
The difference decides whether a reading means anything. Canopy airflow targets sit at the bottom of a vane's range or below it, so a vane can report zero in a room that is moving air exactly as intended. Use a hot-wire probe, held inside the canopy rather than above it.