The method used in this project are as follows: a. Pick a rule with a minimum scale value of 0.5mm. b. Take a picture of this ruler according to the photographing method (zoom-in value is 3.2). c. After taking the photo, draw two parallel lines along the tick marks, and then make another line perpendicular to the two parallel lines. The three lines will produce two intersections, point A and point B of which the real distance is 0.5mm. d. Use Python to measure the pixel difference between the two points A and B, and the pixel difference corresponds to 0.5mm, according to which the scale of the image under the microscope zoom-in value of 3.2 can be determined.