A clock face is the part of an analog clock that displays the time through the use of a fixed numbered dial or dials and moving hands. In its most basic form, recognised universally throughout the world, the dial is numbered 1-12 indicating the hours in a 12-hour cycle, and a short hour hand makes 2 revolutions in a day. A longer minute hand makes one revolution every hour. The face may also include a second hand which makes one revolution per minute, and other hands. The term is also used for the time display on digital clocks and watches.
A second type of clock face is the 24 hour analog dial, widely used in military and other organizations that use 24 hour time. 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. Some special purpose clocks, such as timers and sporting event clocks, are designed for measuring periods less than one hour. Clocks can indicate the hour with Roman numerals or Hindu-Arabic numerals. The two numbering systems have also been used in combination with the prior indicating the hour and the later the minute. Longcase clocks (also known as grandfather clocks) typically use Roman numerals for the hours. ("IIII" -rather than "IV"- is often used to mark the fourth hour to achieve symmetry with "VIII.") Clocks using only Arabic numerals first began to appear in the mid-18th century. The periphery of a clock's face, where the numbers and other graduations appear, is often called the chapter ring.
The clock face is so familiar that, particularly in the case of watches, the numbers are often omitted and replaced with undifferentiated hour marks. Occasionally markings of any sort are dispensed with, and the time is read by the angles of the hands. The face of the Movado "Museum Watch" is known for a single dot at the 12 o'clock position.
Clocks existed before clock faces. The first mechanical clocks were striking clocks: their purpose was to ring bells upon the canonical hours, to call the public to prayer. These were erected as tower clocks in public places, to ensure that the bells were audible. It was not until these mechanical clocks were in place that their creators realized that their wheels could be used to drive an indicator on a dial on the outside of the tower, where it could be widely seen.
Before the late 14th century, a fixed hand (often a carving shaped like a hand) indicated the hour by pointing to numbers on a rotating dial; after this time the current convention of a rotating hand on a fixed dial was adopted. Minute hands (so named because they were the small or minute divisions of the hour) only came into regular use around 1690, after the invention of the pendulum and anchor escapement increased the precision of time-telling enough to justify it. In some precision clocks a third hand, which rotated once a minute, was added in a separate subdial. This was called the 'second-minute' hand (because it measured the secondary minute divisions of the hour), which was shortened to 'second' hand. The convention of the hands moving clockwise evolved in imitation of the sundial. In the Northern hemisphere, where the clock face originated, the shadow of the gnomon on a sundial moves clockwise during the day. This was also why noon or 12 o'clock was conventionally located at the top of the dial.
Until the last quarter of the 17th century hour markings were etched into metal faces and the recesses filled with black wax. Subsequently, higher contrast and improved readability was achieved with white enamel plaques painted with black numbers. Initially, the numbers were printed on small, individual plaques mounted on a brass substructure. This was not a stylistic decision, rather enamel production technology had not yet achieved the ability to create large pieces of enamel. The "13 piece face" was an early attempt to create an entirely white enamel face. As the name suggests, it was composed of 13 enamel plaques: 12 numbered wedges fitted around a circle. The first single piece enamel faces, not unlike those in production today, began to appear c. 1735.