Metric System
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How to define a kilogram

The official kilogram. Credit: BIPM

By Margaret Harris

Pick the correct definition of a kilogram:

a) the mass of a body with a de Broglie wavelength of 6.626069311 × 10^-34 m at a velocity of 1 m/s

b) a mass of a body at rest such that Planck’s constant h is 6.626069311 × 10^-34 Js

c) a mass of exactly 5.0184512725 × 10^25 unbound carbon-12 atoms at rest in their ground state

d) the mass of a lump of platinum-iridium sitting under three vacuum jars in a French laboratory

NIST Metrology Day Celebrates Measurements in the Market

NIST logo USA NIST Metrology

The National Institute of Standards and Technology (NIST) will celebrate World Metrology Day on May 20 by holding a symposium in Gaithersburg, Md. The symposium on “Measurements in Commerce: Metrology Underpinning Economic Development” will emphasize how measurement science and standards play an everyday role in our global economy.


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