1. The Bible, Genesis ph. 5
2. Rashdall, H.: The Universities of Europe in the Middle Ages, p. 150. Clarendon Press, Salerno, Bologna, Paris (1895)
3. Shewhart, W.A.: Economic Control of Quality of Manufactured Products (1931). Reprint p. 51 (2015)
4. Crosby, P.B.: Quality is Free, the Art of Making Quality Certain (1979). Mentor, ISBN: 978–0451621290
5. Feigenbaum, A.V.: Total Quality Control, p. e4 (2004). ISBN: 978–0070220034