What are Classes of Calibration Weights? What's the difference between E1 Class & E2 Class? What is F1 Class, F2 Class and M1 Class Weights?

Ever wondered, how the system of weights in our country has evolved? Was the kilogram standard measure for weighing since earlier times?

What are Standard Weights? How does calibration weights, test weights, standard weights differs? What is the role of E1, E2, F1, F2, M1?