1Comparing and ordering lengths
Use longer/shorter, taller/shorter to compare two lengths directly, then order more than two from shortest to longest.
2Reading a ruler
Line up one end of the object with 0, then read the mark at the other end. Each small division is usually 1 mm.
1 cm=10 mm 3Choosing a sensible unit
mm for very small lengths, cm for everyday objects, m for rooms and buildings, km for journeys and distances between places.
💡Always check the units match before comparing two lengths -- 45 mm and 3 cm can't be compared until one is converted.