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In the tablatures for GC tuning, button 5' is also switched.

The most important consequence is that the G note can be played both pushing (6) and pulling (5').

The same applies to buttons 1 and 1' as to CF tuning. All kinds of variations are possible.
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The note position and the button scheme are shown here.

Click on the images to enlarge them.
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The melodies in GC tuning can also be played on melodeons with a different tuning.

The basses (and chords) can be adjusted according to the scheme in Tablature.