W&H Perfecta 900 Instructions For Use Manual page 27

Operating controls – Changing the speed
By turning the PLUS / MINUS control knob, the values 5 .000 – 80 .000 rpm (LA-66 (optional) 1 .000 – 40 .000 rpm) are
continuously increased / decreased .
Set the speeds from 80 .000 – 100 .000 rpm (LA-66 (optional) 40 .000 – 50 .000 rpm) .
Pre-selected maximum speed must not be exceeded during motor start .

Increase speed .

Press the control knob .

Decrease speed .

Keep the control knob
pressed down and turn it .
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