Question

Why is the SI system a consistent system?

Answer 1

S.I. System is same for all countries, so if any Scientist uses it, then another Scientist from any place around the world can figure it out, that what is he saying, how exactly is the magnitude of the object. That's why it is a Consistent system

Hope this helps!

Answer 2

The SI system or System Internationale is measuring system used around the world with the exception of some previous dominions of the United Kingdoms. 

The units used to meaure fields, like distance is measured in meters (m), translate to all languages with shortcase symbols and the actual unit word having no variency. 

For example :
The unit for luminous intensity in English is candela (cd)
In French the words for luminous intensity is "Intensité lumineuse," however the unit is still candela (cd)
 
SI units are also used as the main components of derived units such as Newtons (N), Omhs (Ω)