Graph Tech Ghost - Manual (Page 22)

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If you prefer to keep your tone control, you can also avoid
drilling a hole for the acoustic volume pot by replacing one of
your pots with a “stacked” or “concentric” pot*. You may choose
to group the magnetic and acoustic volume pots together
on the concentric pot, or group your magnetic volume and
tone on the concentric and convert one of the single pots
into the acoustic volume using the supplied wiring harness.
Replace a Pot with a Stacked Pot
Center shaft
controls
bottom pot
Outer shaft
controls
top pot
* not sold by Graph Tech -- available from most guitar parts suppliers