India adopts new measurement unit for Kilogram, Kelvin, mole, ampere

Filling up your car's fuel tank, checking your blood pressure, navigating using a GPS - daily tasks like these, which have a significant impact on everybody's daily life is based on metrology or the science of measurement.

Starting Monday, the International Metrology Day, the manner in which we measure things - how heavy, how dense, how much and so on - is set to change with a complete revision of the units of measurements, which will be implemented in 101 countries, including India.

Four out of seven base units of the international system of measurement -- kilogram, Kelvin, mole, and ampere- have been redefined and comes into effect across the world today.

In a function held here at CSIR-National Physical Laboratory (CSIR-NPL) today, former BARC director R Chidambaram introduced revised SI units.

The CSIR-NPLI, which is India's National Measurement Institute is now gearing up to incorporate changes in different sectors including the NCERT textbooks and syllabi of metrology courses in engineering.

In order to explain these new definitions of measurements to people, the laboratory has published posters, documents and a textbook.

These changes, however, will not affect the layperson and are more related to the scientific community. A kilogram will still be a kilogram and you definitely will not weigh either less or more than you did yesterday!

The metric system of measurements, also known as the International System of Units (SI) has been in practice since 1889.

In a historic decision on November 16, last year, more than 60 countries unanimously voted to redefine kilogram (SI unit of weight) along with three other units Kelvin (SI unit of temperature), mole (SI unit of amount of substance), and ampere (SI unit of current).

The decision to redefine the four base units was taken at the General Conference on Weights and Measures (CGPM) at an open session of the International Bureau of Weights and Measures (BIPM) in Versailles, France.

There are seven base units of the SI -- second, metre, kilogram, ampere, Kelvin, mole and candela. Some have long been based on physical constants.

For example, the metre has been defined since 1983 as the length of the path travelled by light in vacuum during a time interval of 1/299, 792, 458 seconds.

The kilogram was defined since 1889 by a shiny cylindrical piece of platinum-iridium which is kept in a special glass case, the International Prototype of the Kilogram (IPK), also known as Le Grand K.

The prototype is housed at the BIPM headquarters in Sevres, outside France capital Paris.

But the four SI units that have undergone definition change were previously based on something - i.e. an object, experiment or phenomenon -- which means its values were not universal.

With the new changes, all seven SI units are now defined in terms of physical constants. That means all the units are defined in a common way using what the BIPM calls "the explicit constant" formulation.

"This implementation has now enabled scientists and researchers to base the SI units entirely on fundamental properties of nature, which will ensure their ongoing refinement and improvement for years to come," according to an official statement released by the government.