Footprints

Long before rulers, people measured with body parts. Cubit: from elbow to fingertip (used in ancient Egypt). Handspan: thumb to little finger spread. Foot: length of foot (still used in countries using inches/feet). The problem: everyone's foot is a different size! Two children measuring the same table get different answers. We need a standard unit everyone agrees on.

A centimetre (cm) is a standard unit of length. A ruler has 15 or 30 cm. To measure: place 0 end at start of object, read the number at the end. 100 cm = 1 metre (m). A metre is about the height of a 4-year-old child. Use metre to measure long distances, centimetre for small objects.

To compare: measure both and compare numbers. A pencil = 15 cm. A pen = 14 cm. Pencil is longer! Direct comparison: place side by side. Indirect: measure both, compare numbers. Ordering: arrange from shortest to longest or longest to shortest. Practice: measure your desk, book, and pencil case. Arrange in order.