A set of internationally accepted units to aid in communication of measurements.

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Does the definition of the SI unit “second” require that possible perturbation of primary frequency standards should be measured?

The definition of the SI unit "second" is stated as The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground ...
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What are the proposed realizations in the New SI for the kilogram, ampere, kelvin and mole?

The metrology world is currently in the middle of overhauling the definitions of the SI units to reflect the recent technological advances that enable us to get much more precise values for the ...
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Different units in the equations of electrostatics in macroscopic media

I have the usual equations of electrostatics in macroscopic media expressed in Gaussian units: $$\nabla\cdot\vec{D}=4\pi\rho$$ $$\nabla\times\vec{E}=0$$ $$\vec{D}=\vec{E}+4\pi\vec{P} \tag1$$ My ...