A major advance occurred with the invention of the verge escapement, which made possible the first mechanical clocks around 1300 in Europe, which kept time with oscillating timekeepers like balance wheels.
Spring-driven clocks appeared during the 15th century.
A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation. The development of electronics in the 20th century led to clocks with no clockwork parts at all.
The timekeeping element in every modern clock is a harmonic oscillator, a physical object (resonator) that vibrates or oscillates at a particular frequency.
Pre-modern societies do not have the same precise timekeeping requirements that exist in modern industrial societies, where every hour of work or rest is monitored, and work may start or finish at any time regardless of external conditions.
However, practical limitations, such as that sundials only work well on relatively clear days, and never during the night, encouraged the development of other techniques for measuring and displaying time.
A silent instrument missing such a striking mechanism has traditionally been known as a timepiece.
The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units: the day, the lunar month, and the year.
This object can be a pendulum, a tuning fork, a quartz crystal, or the vibration of electrons in atoms as they emit microwaves. Digital clocks display a numeric representation of time.
Two numeric display formats are commonly used on digital clocks: 24-hour notation and 12-hour notation.