Theory:

Measurements used in olden days:
People lived in olden days used Padi, Uzhakku, Aazhakku, Marakkal, Feet, Handspan and Cubit to measure flowers, rice, millet, cloths etc. But these measures are different from place to place. The Kings foot, the Kings arm and the yard were used as units to measure small length in various places. So to avoid these confusions in measurements, people standardized measurements throughout the world. The standardized measurements are called metric measures. It is defined in $$1971$$, by the General Conference of Weights and Measures.
Measurements used in modern days:
To measure length, we use kilometre, metre, centimetre and millimetre.

To measure weight, we use kilogram, gram and milligram.

To measure volume(capacity), we use kilolitre, litre and millilitre.

To measure time, we use seconds, minutes and hours.

Important!
Metre, Litre, Gram and Seconds are the basic metric units. These unit conversions are based on the decimal system $$(10)$$'s.