A ruler is a simple tool used for measuring length or drawing straight lines. Typically made of wood, plastic, or metal, it usually has markings in centimeters and inches. Rulers are essential in various fields, including art, engineering, and education, helping people create precise measurements and designs. In classrooms, students often use a ruler to help with math problems or to draw neat lines in their notebooks. The concept of a ruler is also related to other measuring tools, such as a tape measure or a caliper, which serve similar purposes in different contexts.