Eric Taylor, The AB Guide to Music Theory PART I, the Associates Board of the Royal Schools of Music(Publishing) Ltd, 1989, Chapter 2: Introduction to Pitch, 2/2 The major scale (P.11-12), Chapter4: More Scales, Keys and Clef, 4/1 Major scales and the circle of fifths, 4/2 Minor scales and keys, 4/3 Relative major/minor keys (P.21-27), ISBN 978-1-85472-446-5