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Equation 1 · Part 6 · The Last Artefact: Redefining the Kilogram

Denominator: 6.62607015 × 10^-34

1 kg=(h6.626 070 15×10−34) m−2 s1\ \mathrm{kg} = \left(\frac{h}{6.626\,070\,15 \times 10^{-34}}\right)\ \mathrm{m^{-2}\,s}
6.626 070 15×10−346.626\,070\,15 \times 10^{-34}

What this part means

The complete quantity below the fraction bar; it must be nonzero for this division.

Its job in the formula

6.62607015 × 10^-34 occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.

The passage around this formula

Inverting that gives the unit explicitly in terms of three fixed constants: 1 kg=(h6.626 070 15×10−34) m−2 s1\ \mathrm{kg} = \left(\frac{h}{6.626\,070\,15 \times 10^{-34}}\right)\ \mathrm{m^{-2}\,s}. which the SI Brochure also writes as approximately 1.475 5214 × 10⁴⁰ times the quantity h ΔνCs divided by c squared [ 1 ] . Notice what the definition does not contain: any apparatus, any material, any temperature, any place. That is the point. “The use of a constant to define a unit disconnects definition from realization”, which “offers the possibility that completely different or new and superior practical realizations can be developed, as technologies evolve, without the need to change the definition” [ 1 ] .

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Learn the underlying idea

A fraction a/b means a divided by b. The top number is the numerator; the bottom number is the denominator, and it cannot be zero.

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Sources cited in the surrounding passage

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