Now available ONLY as a free download from this link: https://aquilacorde.com/gut-strings-and-their-secrets-def-libro-10/
This is a fascinating and very informative booklet about historical instruments, design, and string physics, written by Aquila Corde founder and noted researcher, Mimmo Peruffo. There are many photos, diagrams, and historical references inside.
If you are curious about why instruments were built the way they were, you might find the answer within these pages.
28 pages, 8 1/2 x 11 format.