«Watch». The New Encyclopædia Britannica, 15th Edition4. Encyclopædia Britannica, Inc. 1983. pp. 746-747. ISBN0-85229-400-X. Consultado el 3 de junio de 2012.
Anton, Alex. «Invicta watche». Consultado el 22 de abril de 2021.
nist.gov
«A Revolution in Timekeeping, part 3». A Walk Through Time. NIST (National Inst. of Standards and Technology). 2002. Archivado desde el original el 28 de mayo de 2007. Consultado el 28 de mayo de 2014.
Andrewes, William J. H. (1 de febrero de 2006). «A Chronicle of Timekeeping: Our conception of time depends on the way we measure it». Scientific American. Consultado el 1 de mayo de 2017. «As William J. H. Andrewes (2006) notes: 'In 1675 Huygens devised his next major improvement, the spiral balance spring. (...) The spiral balance spring revolutionized the accuracy of watches, enabling them to keep time to within a minute a day. This advance sparked an almost immediate rise in the market for watches, which were now no longer typically worn on a chain around the neck but were carried in a pocket, a wholly new fashion in clothing.'».
«A Revolution in Timekeeping, part 3». A Walk Through Time. NIST (National Inst. of Standards and Technology). 2002. Archivado desde el original el 28 de mayo de 2007. Consultado el 28 de mayo de 2014.
