What does carbon dioxide actually measure? Use CO2 as a ventilation and occupancy context signal, not as a complete indoor-air-quality diagnosis.
Record the conditions
Keep location, time, weather, occupancy, system state, instrument or observation method and a nearby comparison area with the result.
State the limit
A single reading, photograph, sound or odor description cannot certify a concealed cause. Describe what the evidence directly shows and what remains inferred.
Safe next step
Stop ordinary observation when there is electrical or combustion danger, sewage, unstable materials, unsafe access, rapidly spreading water, suspected hazardous material or acute occupant symptoms. Continue with Carbon dioxide for a repeatable protocol, measurement limit and professional handoff boundary.
Observe→Compare triggers→Repair source→Verify outcome
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