SC401 is Presidential unit, tableptop mounting. 
Press the “ON/OFF” button to activate the microphone.
The luminous ring of the microphone comes on, together with the pilot light associated with this button.
To deactivate the microphone press the “ON/OFF” button again.
This happens independent of the operating mode (automatic / simultaneous) that has been selected. 
To mute the rest of the delegates, press the “CANCEL” button. The pilot light associated with this button comes on, and the 
microphone of the chairman remains in the same state (ON/OFF) in which it was before the priority feature was activated.