Help? What do the different switches mean on my Plantronics Wireless unit?

Q: On the Plantronics Wireless Units (like the CS55) what is the A-B-C-D switch on the bottom of the unit and the 1-2-3-4 switch on the back of the unit? Are these volume control buttons?

A: The A-B-C-D switch is your Outgoing Microphone volume (how people hear you): A is the lowest, D is the highest. The 1-2-3-4 switch is the Incoming Speaker volume (how you hear people): 1 is the highest, 4 is the lowest. You can also use your volume control buttons on your headset to fine tune each one of these settings.