LG TONE Free fit Owner's Manual page 29

Symbols
Refers to alternating current (AC).
Refers to direct current (DC).
0
Refers to class II equipment.
Refers to stand-by.
1
Refers to "ON" (power).
!
Refers to dangerous voltage.
The output level shall automatically return to an output level not exceeding
RS1 when the power is switched off.
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