Source Level Adjustment (Sla) - Pioneer KEH-P5900R Owner's Manual

Source Level Adjustment (SLA)

The SLA (Source Level Adjustment) function prevents radical leaps in volume level when
switching between sources. Settings are based on the FM volume level, which remains
unchanged. (Since the FM volume is the control, SLA is not possible in the FM modes.)
The MW/LW, cassette, CD, External Unit and AUX levels can all be adjusted.

The display shows "+4" – "-4".