The calibration of Sound Level Meters is an essential procedure when carrying out any type of noise survey.  Calibration, both before and after each measurement operation, ensures that the meters are providing consistent and accurate readings.  Users of acoustic equipment are urged to recognize the need for regular field calibration, especially if the method employed to monitor sound levels must meet a recognised standard. An acoustical calibrator should be applied to the microphone to check the correct operation of the measuring instrument.