Tap Tuning related links and other reading material:

• The book Art of Tap Tuning by R H Siminoff is a very good and practical introduction to tap tuning of string instruments

• http://www.platetuning.org/  , http://www.violin.uk.com/ mainly violin related but plenty of reading material and links usefull for the serious guitar builder as well

• For an engineering type of analysis for building guitars and ukuleles the book Left-Brain Lutherie by David C. Hurd is an introduction if you don't mind to see a few equations.

• Howard Wright's PhD Thesis: "The Acoustics and Psychoacoustics of the guitar" http://www.hakwright.co.uk/thesis.html. The thesis requires a good understanding of physics and mathematics and can be downloaded for free.