A clock is an instrument for measuring and indicating the time. The word "clock" is derived ultimately (via Dutch, Northern French, and Medieval Latin) from the Celtic words clagan and clocca meaning "bell". For horologists and other specialists the term "clock" continues to mean exclusively a device with a striking mechanism for announcing intervals of time acoustically, by ringing a bell, a set of chimes, or a gong. A silent instrument lacking such a mechanism has traditionally been known as a timepiece.see Baillie et al., p. 307; Palmer, p. 19; Zea & Cheney, p. 172 In general usage today, however, a "clock" refers to any device for measuring and displaying the time which, unlike a watch, is not worn on the person., London]] History incense clock]] The clock is one of the oldest human inventions, meeting the need to consistently measure intervals of time shorter than the natural units, t