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Equation 1 · Part 3 · The Last Artefact: Redefining the Kilogram

fraction

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}
fraction

What this part means

Divide the expression above the line by the one below it.

Its job in the formula

The expression above the fraction bar is divided by the complete expression below it. The denominator must not be zero.

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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