Difference between local system and si system​

In antiquity, systems of measurement were defined locally: the different units might be defined independently according to the length of a king's thumb or the size of his foot, the length of stride, the length of arm, or maybe the weight of water in a keg of specific size, perhaps itself defined in hands and knuckles.

Systems of Measurement: there are two main systems of measurement in the world: the Metric (or decimal) system and the US standard system. ... The US Standard system uses units that have no predictable relationship to each other. For example, there are 2 cups in a pint, but 4 quarts in a gallon.