Appropriate gearing converts this rotation speed to the correct ones for the hands of the analog clock. The earliest mention of candle clocks comes from a Chinese poem, written in 520 A.D. [citation needed]. The English word "clock" replaced the Old English word daegmael meaning "day measure." In 1735, Harrison built his first chronometer, which he steadily improved on over the next thirty years before submitting it for examination. The apparent position of the Sun in the sky moves over the course of each day, reflecting the rotation of the Earth. During the 15th and 16th centuries, clockmaking flourished. Peter Lightfoot, a 14th-century monk of Glastonbury, built one of the oldest clocks still in existence and continues to be in use at London's Science Museum.

[43], Matthew Norman carriage clock with winding key.

Horton at Bell Telephone Laboratories in Canada. The concentric minute hand was added to the clock by Daniel Quare, a London clockmaker and others, and the second hand was first introduced. A clock with a dial indicating minutes was illustrated in a 1475 manuscript by Paulus Almanus,[50] and some 15th-century clocks in Germany indicated minutes and seconds.

The principles of this type of clocks are described by the mathematician and physicist Hero,[18] who says that some of them work with a chain that turns a gear of the mechanism. An early record of a seconds hand on a clock dates back to about 1560 on a clock now in the Fremersdorf collection.

According to Jocelin of Brakelond, in 1198 during a fire at the abbey of St Edmundsbury (now Bury St Edmunds), the monks 'ran to the clock' to fetch water, indicating that their water clock had a reservoir large enough to help extinguish the occasional fire. Kak, Subhash, Babylonian and Indian Astronomy: Early Connections.

With a piece of string, he attached his pocket watch to his wrist. All modern clocks use oscillation.

Clocks have different ways of displaying the time.

An ideal clock would give the time to unlimited accuracy, but this is not realisable.

The Bundy clock (see image left) was used by Birmingham City Transport to ensure that bus drivers did not depart from outlying termini before the due time; now preserved at Walsall Arboretum. A clock is a device used to measure, keep, and indicate time.

In 1670, William Clement created the anchor escapement,[58] an improvement over Huygens' crown escapement. [52]:417–418[53], During the 15th and 16th centuries, clockmaking flourished, particularly in the metalworking towns of Nuremberg and Augsburg, and in Blois, France. The Warren Clock Company was formed in 1912 and produced a new type of clock run by batteries, prior to that, clocks were either wound or run by weights. In 1714, the British government offered large financial rewards to the value of 20,000 pounds[61] for anyone who could determine longitude accurately. Such mechanisms are usually called timers. According to the poem, the graduated candle, with a measured rate of burn, was a means of determining the time at night. A small clock is often shown in a corner of computer displays, mobile phones and many MP3 players. Bells rang every hour, the number of strokes indicating the time.

Nevertheless, at the end of each period the total time recorded is added up allowing for quicker processing by human resources or payroll. In 1958, IBM's Time Equipment Division was sold to the Simplex Time Recorder Company. Some equipment, including computers, also maintains time and date for use as required; this is referred to as time-of-day clock, and is distinct from the system clock signal, although possibly based on counting its cycles. The primary purpose of a clock is to display the time. The supply current alternates with an accurate frequency of 50 hertz in many countries, and 60 hertz in others. Flip clocks generally do not have electronic mechanisms. For the blind and use over telephones, speaking clocks state the time audibly in words. Shadows cast by stationary objects move correspondingly, so their positions can be used to indicate the time of day. Completely battery-powered portable versions resembling flashlights are also available.

Two numbering systems are in use; 24-hour time notation and 12-hour notation. During the 20th century there was a common misconception that Edward Barlow invented rack and snail striking. They are backed up with software that can be integrated with the human resources department and in some cases payroll software.

Although the mechanisms they use vary, all oscillating clocks, mechanical, digital and atomic, work similarly and can be divided into analogous parts. The Greeks built a water clock, called a clepsydra, where the rising waters would both keep time and eventually hit a mechanical bird that triggered an alarming whistle. Self-calculating machines are similar to basic time clocks. Sundials can be horizontal, vertical, or in other orientations. [47][48][49] The earliest existing spring driven clock is the chamber clock given to Phillip the Good, Duke of Burgundy, around 1430, now in the Germanisches National museum. His patent of 1890 speaks of mechanical time recorders for workers in terms that suggest that earlier recorders already existed, but Bundy's had various improvements; for example, each worker had his own key. Some clocks have both analog and digital displays. Corrections must also be made for the equation of time, and for the difference between the longitudes of the sundial and of the central meridian of the time zone that is being used (i.e. The clock was unrivalled in its use of sophisticated complex gearing, until the mechanical clocks of the mid-14th century. The oldest known sundial is from Egypt it dates back to around 1,500 B.C. Many buildings near major ports used to have (some still do) a large ball mounted on a tower or mast arranged to drop at a pre-determined time, for the same purpose. This problem usually requires expensive biometric devices.

Biometric time clocks are a feature of more advanced time and attendance systems. In Europe, there were the clocks constructed by Richard of Wallingford in St Albans by 1336, and by Giovanni de Dondi in Padua from 1348 to 1364.

A sundial shows the time by displaying the position of a shadow on a (usually) flat surface, which has markings that correspond to the hours.