3 The three elements of any measurement

Every act of measurement involves three things:

1. The physical quantity to be measured (for example the length of a desk, the mass of a stone, the time of a swing).
2. The measuring instrument (ruler, balance, stopwatch, ammeter ...).
3. The unit of measurement — the standard in which the result is expressed.

If any one of the three is missing, the measurement is meaningless. A result such as "mass = 5" is incomplete: is it 5 grams, 5 kilograms or 5 tonnes? Only "5 kg" fully defines the quantity. This is why a number without a unit has no physical meaning.