A clock is simply called a "clock," and all timekeeping devices can be called timekeeping instruments. In modern Chinese, the term "clock" generally has two meanings: one is a general term for all kinds of clocks and watches, and the other specifically refers to larger watches, especially mechanical clocks with a pendulum mechanism.
Clocks are among the earliest inventions of humankind, created to continuously measure time intervals. Some natural time intervals (such as days, leap months, and years) can be observed, while shorter intervals require the use of clocks. Over thousands of years, the principles of timekeeping devices have changed significantly. Sundials use the changing shadows cast by objects on a plane to tell time, and many instruments for calculating time intervals have emerged, including the most well-known hourglass.
Water clocks used in conjunction with sundials are perhaps the earliest timekeeping instruments. Europe invented the escapement in 1300 and later created the first mechanical clock, which could use oscillating timekeeping devices such as a balance wheel.
Wind-driven clocks appeared around the 15th century, and the clockmaking industry began to develop from the 15th to the 16th centuries. The invention of the pendulum clock in 1656 further improved the accuracy of timekeeping. The demand for precise timekeeping in navigation at that time also spurred improvements in the reliability and accuracy of clocks. Electronic clocks were patented in 1840, and the development of electronics in the 20th century led to clocks that could operate entirely without mechanical movements.
The timing element in modern clocks is a resonant oscillator, an object that oscillates at a fixed, precise frequency. A resonant oscillator can be a pendulum, tuning fork, quartz crystal, or the oscillation of electrons in an atom emitting microwaves.
Analog clocks use hands and angles to indicate time, while digital clocks use numbers. There are two time display systems: 12-hour and 24-hour. Most digital clocks use electronic devices and LCD, LED, and vacuum fluorescent displays to show the time. Clock functionality is also a standard feature of modern computers, mobile phones, and tablets.
