Literature summary: the measurand is the quantity intended to be measured, defined specifically enough that different observers understand the same target. 'Room temperature' is incomplete without location, height, time, sensor exposure and operating state.
Instrument resolution, accuracy specification, calibration, drift, placement, stabilization, observer technique and environmental variation can all contribute to uncertainty. A display with more digits does not make the underlying result more certain.
Repeated readings help reveal short-term variation but do not automatically expose systematic effects. Comparison with a reference, calibration information and a defensible method may be needed when the decision margin is small.
Derived results inherit uncertainty from inputs and model. Capacity calculated from airflow and enthalpy difference can be far less certain than either displayed input, particularly when airflow or humidity varies across the stream.