Casio VL-Tone VL-1 Operation Manual page 8

Auto-Power-Off (A.P.O.)
For power economy the unit provides auto-power-off (A.P.O.)
function. If the unit is left with the mode selector turned on, the
A.P.O. function automatically turns off the power in approxi-
mately 6 minutes.
Though the display disappears, the contents of the memory (ac-
cumulated total of the memory calculations or the preset data
of the ADSR and/or the stored melody) are protected. Power is
resumed either by pressing key or by turning off and on.
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