Ruler is the most fundamental measuring tool in mathematics and geometry teaching, usually made of transparent plastic or metal material, with scales in centimeters and millimeters. In teaching, it can be used to measure the length of line segments, draw straight lines, and assist in understanding the concepts of length units such as centimeters and millimeters. By comparing the measurement results of different objects, establish a sense of quantity; When drawing equal length line segments, mathematical relationships such as "equality" and "multiples" should be infused; Combining geometry teaching, drawing edges of regular shapes, annotating lengths to calculate perimeter and area, is an essential tool for mathematics measurement teaching in primary and secondary schools.