(1) Battery check. A battery check shall be conducted on all instruments before field calibration and measurement.

(2) Calibration. Sound level meters shall be field calibrated (using procedures described in the manufacturer's instruction manual) at the beginning and end of each measurement period, and at intervals not exceeding two hours when the instrument is used for more than a two-hour period.

(3) Microphone orientation. The microphone shall be oriented with respect to the sound source as described in the manufacturer's instruction manual.