[charles Tauber]

Originally Posted by surveyor

Here's a chart if you don't want to spend money on a special ruler

http://www.edgeguitarservices.co.uk/nut_space.htm

This is very similar to the method that I use, based on the Theorem of Thales. It can also be adapted to fret position layout for single-scale and multi-scale instruments. If you dig for it, you'll find the method repeated for single-scale fret layout in one of Somogyi's books.