Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The irony of the magnet system for Kibble balances -- a review   The magnet system is an essential component of the Kibble balance, a device
that is used to realize the unit of mass. It is the source of the magnetic
flux, and its importance is captured in the geometric factor $Bl$. Ironically,
the $Bl$ factor cancels out and does not appear in the final Kibble equation.
Nevertheless, care must be taken to design and build the magnet system because
the cancellation is perfect only if the $Bl$ is the same in both modes: the
weighing and velocity mode. This review provides the knowledge necessary to
build a magnetic circuit for the Kibble balance. In addition, this article
discusses the design considerations, parameter optimizations, practical
adjustments to the finished product, and an assessment of systematic
uncertainties associated with the magnet system.

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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
4
The categories of this paper are: cond-mat
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
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The categories of this paper are: acc-phys
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The categories of this paper are: atom-ph
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The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: econ
37
The categories of this paper are: supr-con