Outside-air quantities are influenced by more than a single damper position. A defensible test considers the full airside system and the operating mode present during measurement.
Choose the right operating condition
Document fan speed, economizer mode, relief or exhaust operation, building pressure, and expected occupancy condition before interpreting outside-air readings.
Use a suitable measurement method
Intake geometry, turbulence, access, and low velocity can affect accuracy. The selected method should match the conditions and acknowledge practical limitations.