This book is about a new 12 notes per octave tuning called Eagle 53. This tuning was designed to improve on, and replace, the standard Western tuning: 12 Tone Equal Temperament. Some notes are higher than usual and others are lower in varying degrees. Many chords and scales are more in tune and some new and exotic chords and scales occur as well. Eagle 53 tuning is suitable for pianos and MIDI keyboards that can be retuned with the right software and for guitars and other stringed and fretted instruments (which need refretting to accommodate the new tuning). This book describes how the author worked it out, the rationale and mathematics behind Eagle 53. Eagle 53 is a slightly tempered version of a just tuning, Eagle J.I. which looks like this: 1/1, 16/15, 9/8, 6/5, 5/4, 4/3, 7/5, 3/2, 8/5, 5/3, 9/5, 15/8, 2/1 The '53' refers to 53EDO (53 Equal Divisions of the Octave). Eagle 53 is a 12 note subset of 53EDO. The author's web site has music, pictures and information related to Eagle 53. For the web site address (if you are on an Amazon page) see the "More about the author > Biography" section below. Click on "Visit Amazon's John O'Sullivan Page" in this section to see a video of the author playing an Eagle 53 guitar. There is a condensed, older and cheaper eBook version of this book available on Amazon. The title of the eBook is: Eagle 53 Musical Tuning. ASIN: B07DKTK9DX For guitarists check out The Eagle 53 Guitarist Deluxe Second Edition ISBN 9780956649287.