Measuring segments
Units of length: 1 km = 1000 m, 1 dm = 0.1 m, 1 cm = 0.01 m, 1 mm = 0.001 m. The value of a segment’s length depends on the chosen unit: AB = 5 cm = 50 mm. We measure length with a ruler, tape measure, tailor’s tape, calipers, and in surveying with electronic instruments. On a map, distances are found by the scale: if 1 cm on the map means 100 km, a 4 cm segment on the map stands for 400 km. Measuring on a map is only approximate because the Earth is not flat and cities are not points. Some countries use units such as 1 inch = 2.54 cm and 1 mile = 1.609 km.
“Span and pace”: each pupil measures their own hand span and pace with a ruler, then measures the desk in spans and converts to centimetres. Work only inside the classroom or another safe place.