Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The kilogram: inertial or gravitational mass?   With the redefinition of the international system of units, the value of the
Planck constant was fixed, similarly to the values of the unperturbed
ground-state hyperfine transition frequency of the $^{133}$Cs atom, speed of
light in vacuum. Theoretically and differently from the past, the kilogram is
now explicitly defined as the unit of inertial mass. Experimentally, the
kilogram is realized by atom count or the Kibble balance. We show that only the
former method measures the inertial mass without assuming the universality of
free fall. Therefore, the agreement between the two measures can be interpreted
as a test of the equivalence principle.

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The categories of this paper are: cmp-lg
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The categories of this paper are: funct-an
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The categories of this paper are: supr-con
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The categories of this paper are: cond-mat
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-alg
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The categories of this paper are: nlin
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: acc-phys
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: gr-qc