Answer:
The irrevocable utility of the units comes from the scientific world, but also from the economic and commercial world, which require a simple and fixed reference for their correct functioning.
But we see in history, that the units have multiplied and the will for universality and simplicity have rarely been a reality since the divergences of interest helping, the measurements were for a long time related to a multitude of standards, different according to the place, the time and the nature of the product, the reference often having a complex definition, the standard was difficult to reproduce and therefore the measurements not very precise, which unfortunately led to misunderstandings and inconsistencies.
A unit of measurement is defined by a standard, the standards must have the following qualities:
- maximum precision (determining factor because the standard can therefore change if technology evolves and finds a more precise one)
- natural and invariant character (in time and space)
- reproducible
remark: the defining relations are arbitrary, and the universality of the standard can only result from a convention between men.