Suggestions for fret placement from Bart Hopkin's book

Hi Folks,

I apologize if someone already mentioned this, but as I was flipping
through Bart Hopkin's "Musical Instrument Design: Practical Information
for Instrument Making" book and day-dreaming yesterday, I came across a
couple of suggestions he made for calculating better fret placement:

* On an otherwise complete (and strung) but unfretted instrument, find
the position that gives a true octave when the string is pressed to
the fretboard. Multiple the active string length by two to get the
effective string length to use for fret calculation with whatever
ratios you want.

* For a 12-TET fretboard he mentions a "rule of 18" in which each fret
is placed 1/18th of the remaining string length away from the
previous fret. This apparently has the effect of compensating for
the change in tension when pressing the string to the fretboard.

For comparison:
2^(-1/12) = 0.943874312681693...
17/18 = 0.944444444444444...

Cheers,
Christopher