Hello everyone. As far as I know, any unit can be expressed in terms of basic units: time, length and mass. It quite clear that we could choose them differently but in any case we get three units as the base.. And I ask: Why? What fundamental properties of nater make it It happens that any physical unit in this crazy being can be derived from exactly 3 base unit? Why 2 isn't enough? Why not 5? What is the origin, what is behind it?