Sennheiser System 2015 Instructions For Use Manual page 14

Display for microphone level
The display for microphone level (MIC) shows the level of the connected
microphone. The display should show full deflection only when you speak
very loudly.
Display for lock mode
If the lock mode is activated, the lock mode icon appears on the standard
display. If the lock mode is deactivated, the lock mode icon disappears from
the standard display.
Display backlighting
After pressing a button, the display remains backlit for approx. 15 seconds.
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