1967. Revised edition. 126 pages. No dust jacket. Pictorial cloth covered boards. Black and white diagrams throughout. Pages remain bright and clean with minimal tanning and foxing. Binding remains firm. Rear free endpaper torn out resulting in some loss to surface of pastedown. Boards have moderate shelf wear with mild bumping and fraying to corners and crushing and fraying to spine ends. Spine noticeably tanned. Some additional mild marks and staining.