Prism and lens making: A textbook for optical glassworks - Frank Twyman, 1988 (2nd edn). 629 pp. 0-85274-150-2. Price: £25 (paperback) - Tyrer, J. (Elsevier)
http://linkinghub.elsevier.com/retrieve/pii/0143-8166(89)90027-4
Keywords: ZN; ZL; U; ZG