World gets the redefined units of measurement of kilogram, Kelvin, mole and ampere

World gets the redefined units of measurement of kilogram

Question: What was the date for the worldwide implementation of all the changed SI units?
(a) 19th May, 2019
(b) 20th May, 2019
(c) 21st May, 2019
(d) 18th May, 2019
Answer: (b)
Related facts:

  • After decades of ground-breaking laboratory works, the world’s scientific and technical community, in a landmark and historic decision taken in the recent open session of the General Conference on Weights and Measures (CGPM) at BIPM on 16th November, 2018, has unanimously adopted the resolution to redefine four of the seven base units.
  • This includes the kilogram (SI unit of weight), Kelvin (SI unit of temperature), mole (SI unit of amount of substance), and ampere (SI unit of current).
  • This decision 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.
  • The fundamental constants are invariants of time and space and successfully replaced the artifact based units, and aptly opened up the new era for quantum world by linking all seven base units to fundamental constants/quantum standards.

Implementation of new SI units:

  • The new SI is being implemented worldwide from 20th May, 2019, i.e. the World Metrology Day. The World Metrology Day (WMD) is celebrated annually on this very day as the Meter Convention was signed by representatives of seventeen nations on 20th May, 1875.
  • The Convention set the framework for global collaboration in the science of measurement and in its industrial, commercial and societal applications.
  • The whole metrology world, especially the National Metrology Institutes (NMIs) are celebrating this year’s WMD as mark for the new beginning of metrology, based on constant of nature on a large scale.
  • CSIR-NPL, the NMI of India have kept the strides going in these fields and started the R&D efforts in establishing the new SI, alongside the international implementations from 20th May, 2019.


  • On this historic day, CSIR-NPL introduced redefined SI Units to nation in terms of constant of nature through a series of events, delivering lectures, releasing theme (The International System of Units – Fundamentally Better) based poster of BIPM etc.
  • As a national responsibility and keeping in view of the importance and recognition of new revision of SI, the CSIR-NPL has also prepared documents on
  • NPL Policy on Metrological Traceability;
  • Recommendations on the proposed changes to be incorporated in the National Council of Educational Research and Training (NCERT), New Delhi textbooks;
  • Recommendations on the proposed changes to be incorporated in syllabi of metrology courses in graduate engineering and academic courses.
  • On this occasion CSIR-NPL also published a book entitled, “Redefined SI Units and Glimpses of NPL Metrological Activities”.


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