When manufacturing machine parts, it must be processed according to the size numbers marked in the drawings, and it is not allowed to directly measure the size of the graphics from the drawings. The technical conditions that must be met in mechanical manufacturing, such as tolerances and fits, form and position tolerances, surface roughness, materials and heat treatment requirements, etc., should be marked with symbols, words and numbers in the drawings in accordance with the mechanical drawing standards. Before the 20th century, the drawings were drawn by hand using common drawing tools. At the beginning of the 20th century, a drawing machine with a mechanical structure appeared, which improved the efficiency of drawing. Computer graphics appeared in the second half of the 20th century. The patterns that need to be drawn were compiled into a program and input into an electronic computer. The computer converted it into graphic information and sent it to a plotter to draw the pattern, or sent it to a computer-controlled automatic machine tool for processing.