🔹Fundamental units: Fundamental units are units which are independent of each other and have their own standard (base).
🔹Derived units: Derived units are units which are not having their own standard (base) and are obtained from fundamental units.
🔹SI unit: In 1960, the new system of units – the SI units – was introduced.
🔹Units should be well-defined, reproducible, comparative, sensitive, objective, repeatable and linear.
🔹Air is used as the measurement material due to its availability, reproducibility, accuracy and sensitivity and its atomic number.
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