A ruler is a tool we use to measure the length of things using a unit called the “centimeter” (cm), marked with small, evenly spaced lines that help us measure precisely.
To measure something with a ruler, follow two key steps: first, line up the start of the object exactly with the zero mark on the ruler. Second, look at the number where the object ends — that number is its length in centimeters.
Example: if we place a pencil so its end starts at zero, and its tip ends at the number 15, the pencil is 15 centimeters long. It's important to always start measuring from the zero mark, not the edge of the ruler, since some rulers leave a small gap before the zero.
