Two instruments disagree. Which reading is right?
An outdoor sensor reports a different temperature from a nearby reference instrument. The difference might indicate drift, poor placement or a genuine local microclimate. The gold standard is a controlled comparison that distinguishes these possibilities.
Define the comparison objective
A reference check for calibration differs from a comparison of two urban locations. Decide which question is being answered.
Use suitable reference equipment
Reference instruments and procedures should be appropriate for the measurement and required accuracy.
Control environmental differences
Height, shade, ventilation and nearby surfaces can affect readings. Co-location or other suitable arrangements may be needed for a meaningful comparison.
Synchronise observation times
Comparing readings taken at different times can create apparent discrepancies during rapidly changing conditions.
Analyse bias and variability
Look for consistent offsets, drift and changing differences rather than relying on one paired reading.
Document corrections
Record the method, equipment, findings and any resulting calibration or data-quality decisions.
Break-test: agreement improves after moving a sensor
Can the team distinguish the placement effect from a change in instrument performance?
Connected knowledge
See Sensor Drift Monitoring, Microclimate Sensor Calibration and NEA.