clock

A clock is a device for measuring, displaying and keeping time. It can be mechanical, electronic, or atomic. The word clock derives from the Dutch klok, meaning bell or timepiece; modern usage covers devices that show hours, minutes, and sometimes seconds, and may include additional displays or functions.

Historically, timekeeping began with solar and water clocks in ancient civilizations. Mechanical clocks appeared in medieval Europe, using a verge escapement and gear train to move hands on a dial. The invention of the pendulum clock by Christiaan Huygens in 1656 greatly improved accuracy. Spring-driven mechanisms enabled portable clocks and watches, spreading timekeeping beyond towers and walls. In the 20th century, quartz crystal oscillators offered high precision and low cost, leading to widespread electronic clocks. Since the mid-20th century, atomic clocks have defined the SI second and underpin global time standards.

Clocks come in analog and digital forms. Analog clocks display time with a dial and rotating hands; digital clocks show numerals. Core components of mechanical clocks include a power source (weights or springs), a gear train, an escapement to regulate motion, and an oscillator (pendulum or balance wheel). Electronic clocks rely on quartz crystals or integrated circuits, while atomic clocks use microwaves interacting with atoms such as cesium or rubidium to maintain extreme accuracy.

Modern clocks support daily life, scheduling, navigation, broadcasting, science, and industry. They are synchronized with international time standards, notably Coordinated Universal Time (UTC), to coordinate activities globally. Advances continue toward greater stability, network synchronization, and integration with other devices.