The reason that layout was a reject is because there’s too much space between the last knob and the end of the guitar…
So erase . . and a re-do is in order….
It’s looking pretty close here, so I’m sticking with this one…
Again using a straightedge and the photo, I determine that a line running from the apex of the curve formed by the bottom horn, actually the only horn, extended through the center of the switch knob intersects the neck at about the 18th fret…. Therefore I extrapolate and layout a corresponding line on the guitar.
When a center mark is place and the knob’s diameter is drawn I can see it appears a bit too far forward, so I relocate it about 3/16 back… that looks about right.
I take an awl and mark the locations…
Ron Kirn