Clock

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A clock is a device that tells the time. Some clocks can only show the time. Other clocks can show other things. For example, some clocks can show the date as well as the time, or show other information, like the timer, temperature or the weather, some have stopwatch and some have alarm.

Keeping time

Clocks use different ways to measure time. Clocks need some sort of steady beat or motion to track the change in time. Ancient water clocks worked by the steady movement of water from a container with a hole in the bottom to another container without a hole. Other clocks use pendulums, springs and gears to track the change in time correctly.

Digital clocks work by measuring the vibrations of quartz crystals when charged with electricity. The vibration frequency of the crystal does not change.

Atomic clocks use the electromagnetic waves absorbed and emitted by atoms such as caesium to measure time. They are the most precise clocks in the world.

Clock displays

The two most common types of displays on clocks are "analog" and "digital".

Digital clocks

Digital clocks use numbers to show the time. LCDs and LEDs are common for digital clocks. Unlike analog clocks which are based on 12 hours, digital clocks can use either a 12-hour clock (often with am for postmidnight/morning and pm for afternoon/evening) or a 24-hour clock. Digital clocks are usually smaller and easier to both use and read than analog clocks but they can also be made much larger. New digital clocks can even correct themselves using the internet or radio signals.

Sounds

There are also clocks that use sound, usually along with a dial or some other means, to show the time. The sound could be as simple as a bell or so complex that it sounds the same as a person. Many clocks that do this are old and are driven by springs or weights rather than batteries or other forms of electric power. Some special clocks are often used by people who are blind or cannot see well enough to read an analog or digital clock. They can also be used by people with mental problems that cause them to be unable to read other clocks.

Types of clocks

There are many different types of clocks and watches. They are different in what they are used for, what they can do or how they are made. Examples include:

• A watch, also called a watch, is worn on the wrist. It is held in place by two straps connected to the watch, and then wrapped around the wrist and connected to each other.
• A pocket watch is kept in a pocket. It usually has a small chainor a chain like cloth which is connected to the person's clothing. This helps people to not lose the watch.
• A radio (controlled) clock is automatically synchronized to a time, transmitted by a radio transmitter. JUNGHANS MEGA is the name of the world's first radio-controlled wristwatch with hands.
• A sundial is an old form of a clock which uses the Sun to tell time.
• An alarm clock is a clock that makes a sound (often a buzzing or a bell-like sound) or plays music at a certain time. It is used by people to wake up from sleep at a time they choose.
• A grandfather clock is a tall clock that stands on a floor. It uses a pendulum to tell time.
• A cuckoo clock is a pendulum based clock which makes a sound each hour on the hour. They often also have a small door. When the clock makes the sound, the door opens and a small toy bird or other item usually comes out of the door.
• An hourglass, also called a sandglass or sand timer, uses sand trickling slowly to measure time.

Formats of times

• LT = Legal Time.
• AM = Ante Meridiem.
• PM = Post Meridiem.