# Particle Counter Technology – ISO 21501-4 Calibration Standard and its significance in data accuracy

ISO 21501-4  (Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness by particle concentration) requires airborne particle counter calibrations to be completed following ISO 21501-4. The table below defines the parameters of ISO 21501-4.

By calibrating particle counters following ISO 21501-4 the end result is a higher accuracy calibration. If the particle counter is passing an ISO 21501 calibration you can be assured that the sensor is operating correctly and the particle count data is accurate.