coefficient of expansion is the quadratic coefficient of expansion References . Has detailed account of development of balance spring. . . Detailed section on balance temperature error and auxiliary compensation. . Good engineering overview of development of clock and watch escapements, focusing on sources of error. . Comprehensive 616 p. book by astronomy professor, good account of origin of clock parts, but historical research dated. Long bibliography. . Detailed illustrations of parts of a modern watch, on watch repair website . Technical article on construction of watch balance wheels, starting with compensation balances, by a professional watchmaker, on a watch repair website. External links Video of antique mid-19th century watch showing the balance wheel turning History of watches, on commercial website. Monochrome-Watches A technical perspective the regulating organ of the watch Oliver Mundy, The Watch Cabinet Pictures of a private collection of antique watches from 1710 to 1908, showing many different varieties of balance wheel. Footnotes Timekeeping components