To measure a physical quantity, we need to compare it with a known fixed physical quantity of the same kind, i.e., a unit. Hence, the measurement of a physical quantity is always written as a combination of a numeral along with the unit. The numeral specifies the number of times the unit is repeated. Example:
1. Using a centimetre scale, the length of pencil box is found to be 20 centimeters (cm). 20 cm simply means that the length is 20 times a centimetre. (The centimetre forms the unit of length in a centimetre scale.) Here, the number 20 is the numeral (magnitude) and cm is the unit.
2. Using a weighing (kilogram) scale, the weight of the box is found to be 2 kilograms (kg) 2 kg simply means that the mass of the box is 2 times a kilogram. (The kilogram forms the unit of mass in a kilogram scale). Here, the number 2 is the numeral (magnitude) and kg is the unit.
