Kawai PN300 Owner's Manual page 30

Make sure that the piano is in the programming mode.
Press the METRONOME button.
The metronome will sound in four-four time.
The PIANO 1 LED will be turned off and in turn, the METRONOME LED will flash.
Now you can start setting the metronome volume.
Set the degree of volume change for the metronome.
Use the seven white keys at the left end of the keyboard to set the degree of volume.
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Leave the programming mode.
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