Volume Control
Adjust the volume to the most comfortable listening level by moving the volume control slide switch.
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Boost Button (HA-40 only)
Press and hold down the Boost button for more amplification. It also eliminates any background noise and feedback by muting the microphone in your handset. You must remember to release the button when you speak so that the other party can hear you, then press and hold the boost button again when they speak.
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