Why mks system had to be rationalised to obtain SI?

The International System is now internationally recognised - its advantages over the CGS and other metric systems are such that all countries that were using the older units have changed to the new system.

SI is a logically developed system of measurement in which all units have been designed so that the relationship between them is as simple as possible. Thus, units derived by combinations of other SI units are themselves SI units; there are no odd conversion factors between SI units. This property is known as the coherence of the system and in this respect SI is superior to older metric systems.