PCE Instruments PCE-322A Instruction Manual page 12

"A/C" Frequency weighting select button
A：A-Weighting
C：C-Weighting
"HOLD" button:
Press "HOLD" button, The hold function freezes the
reading in the display.
Power button
Turn the meter power ON/OFF
External DC 9V power supply terminal
For connection with DC 9V power supply.
Aperture size: external diameter: 3.5mm, internal
diameter: 1.35mm
USB interface
USB signal output is a 9600 bps serial interface.
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