Yamaha PORTATONE PSR-110 Owner's Manual page 7

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Using the Auto Accomp.
Function/Multi Fingering
Note:
In Single Finger, the AUTO ACCOMP. SECTION is set
vetween the СІ key (the lowest key) and the C#2 key.
C7
Press the root note
together with any black key
to the left of it.
Press the root note together
with any white and black
key to the left of it (three
keys altogether).
Note:
The "black key" keys follow the same rules; for example, Bb7
could be played as Bb and A (the white key to the left of it).