# `Cldr.UnknownNumberSystemError`
[🔗](https://github.com/elixir-cldr/cldr/blob/v2.47.4/lib/cldr/exception.ex#L13)

Exception raised when an attempt is made to use a number system that is not known
in `Cldr`.  `Cldr.Number.number_system_names/0` returns the number system names known to `Cldr`.

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*Consult [api-reference.md](api-reference.md) for complete listing*