See also:

Telephone
...

Service booklet
Perform maintenance work at the service center, and record the work in the service booklet. The entries are proof of regular maintenance. ...

Treble, bass, balance, and fader
▷ "Treble": treble adjustment. ▷ "Bass": depth adjustment. ▷ "Balance": left/right volume distribution. ▷ "Fader": front/rear volume ...