Question

does the standard unit vary from person to person.

Answer 1

Standard units are those which are used by people as a common standard unit of measurement, and do not vary from person to person.

The internationally accepted standard units are the SI units. The International System of Units, universally known as the SI (from the French Systeme International d’Unites) is necessary because lack of standard unit of measurement would cause confusion and a waste of time in converting from one unit to another all the time. So, the SI system is adopted all over the world as the standard measurement unit system.