<P> 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, or with non-numeric indicator marks . The two numbering systems have also been used in combination, with the prior indicating the hour and the later the minute . Longcase clocks (grandfather clocks) typically use Roman numerals for the hours . Clocks using only Arabic numerals first began to appear in the mid-18th century . </P> <P> The periphery of a clock's face, where the numbers and other graduations appear, is often called the chapter ring . </P> <P> The clock face is so familiar that the numbers are often omitted and replaced with undifferentiated hour marks, particularly in the case of watches . 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 . </P> <P> 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 time is read by observing the placement of several "hands" which emanate from the centre of the dial: </P>

What are three small dials on a watch face