Compare indoor dew point with the temperature of the affected surface.
What this check can reveal
The useful result is a condensation risk. 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.