1968. Third Edition. 346 pages. No dust jacket. Purple Paper covered boards with traces of tape & small sticker to front pastedowns. Contains black & white diagrams. Pages remain bright with minimal tanning. Text is clear. Binding remains firm. Boards have moderate edge-wear with bumping to corners and rubbing to surfaces. Slight tanning and scuffing to spine and edges with crushing to spine ends. Lettering is bright and clear to front board.