![]() These were tower clocks installed in bell towers in public places, to ensure that the bells were audible over a wide area. ![]() The first mechanical clocks, built in 13th-century Europe, were striking clocks: their purpose was to ring bells upon the canonical hours, to call the local community to prayer. Clocks spread to England from the Low Countries, so the English word came from the Middle Low German and Middle Dutch Klocke. The word clock derives from the medieval Latin word for "bell" clocca, and has cognates in many European languages. It starts from "12" at midnight, makes one rotation until it is pointing at "12" again at noon, and then makes another rotation until it is pointing at "12" again at midnight of the next morning.ġ5th-century rotating dial clock face, St. The hour hand moves slowest of all, taking twelve hours (half a day) to make a complete rotation.For every rotation of the minute hand, the hour hand will move from one hour mark to the next. It takes one hour (sixty minutes) to make a complete rotation from 12 to 12. The minute hand rotates more slowly around the dial.For every rotation of the second hand, the minute hand will move from one minute mark to the next. The second, or sweep, hand moves relatively quickly, taking a full minute (sixty seconds) to make a complete rotation from 12 to 12.On some models, a very thin "second" or "sweep" handĪll three hands continuously rotate around the dial in a clockwise direction – in the direction of increasing numbers.The time is read by observing the placement of several "hands", which emanate from the centre of the dial: Most modern clocks have the numbers 1 through 12 printed at equally spaced intervals around the periphery of the face with the 12 at the top, indicating the hour, and on many models, sixty dots or lines evenly spaced in a ring around the outside of the dial, indicating minutes and seconds. The green and red shaded areas denote 3 minute periods during which radio silence was maintained to facilitate listening for distress calls at 2182 kHz and 500 kHz respectively. Reading a modern clock face Ī ship's radio room wall clock during the age of wireless telegraphy showing '10:09' and 36 seconds'. Occasionally, markings of any sort are dispensed with, and the time is read by the angles of the hands. The clock face is so familiar that the numbers are often omitted and replaced with unlabeled graduations (marks), particularly in the case of watches. Clocks using only Arabic numerals first began to appear in the mid-18th century. Longcase clocks (grandfather clocks) typically use Roman numerals for the hours. The two numbering systems have also been used in combination, with the prior indicating the hour and the latter the minute. Clocks can indicate the hour with Roman numerals or Hindu–Arabic numerals, or with non-numeric indicator marks. Some special-purpose clocks, such as timers and sporting event clocks, are designed for measuring periods less than one hour. This is similar to the 12-hour dial above, except it has hours numbered 1–24 around the outside, and the hour hand makes only one revolution per day. The term is less commonly used for the time display on digital clocks and watches.Ī second type of clock face is the 24-hour analog dial, widely used in military and other organizations that use 24-hour time. The face may also include a second hand, which makes one revolution per minute. A long minute hand makes one revolution every hour. In its most basic, globally recognized form, the periphery of the dial is numbered 1 through 12 indicating the hours in a 12-hour cycle, and a short hour hand makes two revolutions in a day. A clock face is the part of an analog clock (or watch) that displays time through the use of a flat dial with reference marks, and revolving pointers turning on concentric shafts at the center, called hands.
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