In the second grade, students used a student's ruler, which was 25 cm long. There are two kinds: a rigid ruler made of plastic and a flexible ruler that can be folded. It is also twenty centimeters long.

In the second grade, I began to learn a quantity, and the unit of learning length is meters and centimeters. Ask the students to measure the length and width of books and exercise books and the height of desks with a ruler (also in centimeters). For example, measure the length and width of a classroom in meters.