Extech Instruments 407790A, User Manual, Page: 49 / 55

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407790A-EN_V2.4 1/20
8. Calibration
Calibrating the 407790A requires an acoustical calibrator such as the Extech Model 407766 or
407744 that can provide 94.0dB or 114dB at 1kHz.
1. Set the power switch to the OFF position.
2. Press and hold the

+
and

-
buttons then turn the power ON until CAL appears on the
screen.
3. Insert the microphone into the opening of the acoustical calibrator.
4. Switch the calibrator ON (1kHZ 94dB or 114dB)
5. Use the

+
and

-
buttons to adjust the reading of the meter to match the sound
calibrator’s output value. (adjust range from -12.8 to 12.7dB).
6. Press the

button to store the calibrated value.
7. Switch the calibrator and sound meter OFF.
8. Remove the calibrator from the microphone very slowly to avoid damaging the
microphone.