Clock

A clock (from the Latin cloca, "bell") is an instrument for measuring time. A clock is usually a physical instrument; an especially accurate one is called a chronometer. The clock in its modern form (24 hour clock) has been in use since at least the 14th century. Clock can refer to an abstract system of time measurement (see calendar for other measurements). Modern clocks define constant units of time: an hour is always sixty minutes, of sixty seconds each.

External links

• American Watchmakers-Clockmakers Institute
• British Horological Institute
• 24 hour analog clocks
• Science Museum - more details on early clocks
• Humanclock.com a website with a unique image for every minute of the day
• http://www.ieee-uffc.org/freqcontrol/marrison/Marrison.html article, by a key figure in the development of quartz crystal clocks, on the history of timekeeping up to the late 1940s (based on remarks he made when given a prize for his contributions to horology) from The Bell System Technical Journal, Vol. XXVII, pp. 510-588, 1948