The traditional units were not uniform as the length of a cubit, foot and handspan varied from person to person according to their body size. Similarly, there was no certainty that all grains were exactly the same weight. So these units could not be used for scientific measurements where accuracy was a prime concern. The development of a large number of systems of measurement also made it very difficult to conduct trade and commerce between different socities. Therefore, people felt the need to have standard units which could be used for accurate measurement and were accepted universally.
