Use a safe lightweight indicator to see which way air moves at a doorway or grille.
What this check can reveal
The useful result is a pressure direction. It narrows the next step but does not prove every hidden condition.
How to record it
Write down the date, location, environmental conditions and a nearby reference. Repeat the check under the condition that normally triggers the symptom.
Common interpretation error
Do not turn one reading into a diagnosis. Compare patterns, repeatability and independent clues.
Observe→Distinguish→Control source→Verify
Living dossierPublished knowledge is connected and improved as new cases, images and outcomes are added. Updated 2026-07-20.
