Fan assembly

A fan assembly comprising:

• a motor-driven impeller arranged to generate an airflow;
• an air outlet arranged to emit the airflow from the fan assembly;
• a plurality of sensors arranged to measure a value for each of a plurality of air quality characteristics;
• a display arranged to present data to a user of the fan assembly;
• and
• a processor configured to:
• receive, from the plurality of sensors, measured values for each of the plurality of air quality characteristics;
• for each of the plurality of air quality characteristics, identify one of a corresponding set of intervals within which the measured value falls and select an air quality index value associated with the identified interval;
• identify the highest of the selected air quality index values as a current overall air quality index value;
• and
• cause the display to display a time series plot of the current overall air quality index value and a number of preceding overall air quality index values.