The length integral of the edge around a finite area is called the perimeter, which is the length of a graph. The perimeter of a polygon is also equal to the sum of all sides of a graph, the perimeter of a circle =πd=2πr (d is the diameter, R is the radius, π), and the perimeter of a sector = 2R+nπR÷ 180? (n= central angle) = 2R+kR (k= radian).

If it is a triangle with the same area, the perimeter of an equilateral triangle is the shortest; If it is a quadrilateral with the same area, the perimeter of the square is the shortest; If pentagons with the same area are used, the perimeter of regular pentagons is the shortest; If you use any polygon with the same area, the circumference of a regular circle is the shortest.

Perimeter can only be used on two-dimensional figures (planes and surfaces), and three-dimensional figures (solids) such as cylinders, cones and spheres can't express their boundary size by perimeter, but by total surface area. Total surface area = the total area of all sides of a solid.

With the development of society, a variety of instruments have been born, which are designed to meet the needs of people's real life and work. The perimeter and area measuring instrument is no exception, and its purpose is to help people measure the perimeter and area of any plane figure conveniently, quickly and accurately.