We usually think of a clock as a physical thing, like an alarm clock or a wristwatch. But a clock is really a process embodied in a machine, and the nature of that process is repetitive.
(A)
Indeed, it is almost impossible to think of a clock that does not depend on a repetitive cycle of events. The only example that comes to mind readily is a candle marked in hours. But here too there is iteration ― the repeated burning of molecules of wax ― so this too is an iterative process, although at first masked.
(B)
The use of radiocarbon dating is another, much longer scale clock that also appears to be like this. It seems to yield a smooth time scale but in fact does not: the decay of atoms of carbon-14 is repetitive, although on a large scale it gives the appearance of being continuous.
(C)
A clock can be almost any process that repeats itself over and over again for an indefinite period. Water clocks drip at a steady pace; quartz crystals vibrate regularly.
* molecule: 분자 ** quartz: 석영(石英)
