Q. Assertion : S.I. units are logical and coherent.
Reason : S.I. system of units is a rationalised system.

 2541  237 AIIMSAIIMS 2002Physical World, Units and Measurements Report Error

Solution:

A coherent system means a system based on a certain set of basic units from which all derived units are obtained by multiplication or division without introducing numerical factors. In S.I. system of units, heat energy, electric energy and mechanical energy are measured in joule . But in . system, they have different units.