In mathematics, a clock refers to a plane figure that moves around a fixed path. Generally speaking, we can regard the clock face as a circle, and the number of clocks refers to the path of choosing a point from the boundary of the circle as the starting point of movement and returning to that point after a period of time.

The definition of Bell number has applications in analytic geometry, calculus and complex variable functions. In analytic geometry, we can get the area and perimeter of parabola, ellipse, hyperbola and other figures through the trajectory of the clock. In calculus, bell is used to solve definite integral and calculate the length of curve. In the complex variable function, Bell number refers to the path describing the arc on the complex plane.

In addition to the field of mathematics, bells are also widely used in daily life. We can see that the clocks in the street are all designed according to the bell number. In addition, in musicology, the number of clocks is also used to indicate the rhythm or tone change in music.

In a word, the clock, as a plane motion figure, is widely used in mathematics, physics, music and other fields. Its importance lies in that it can not only describe complex graphics, but also be the basis of some calculation problems.