Rulers are also called measuring rulers and scales, which are tools used to draw line segments (especially straight ones) and measure length. There are usually scales on the ruler to measure the length.
Some rulers leave a special shape such as a letter or a circular hole in the middle, which is convenient for users to draw pictures. They are usually used to measure and calculate the length. They are generally divided into tape measure, vernier caliper, square ruler, and ruler.
Rulers are usually made of plastic, iron, stainless steel, plexiglass, etc.