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This category collects pages that use the formatnum parser function with a non-numeric or incorrectly formatted value, e.g. ((formatnum:foo)) or ((formatnum:12,345)).

Ways to fix or work around this error inside template code:

• If formatnum is being applied to a string that includes both a number and words, change it to wrap just the number. Example: ((formatnum:(({var))} dollars)) → ((formatnum:(({var))))} dollars
• Another way to work around invalid input is to remove commas from the input like this: ((formatnum:((replace|(({var))}|,|)))). Note that input using commas as decimal separators, in contravention of MOS:DECIMAL, will cause formatnum to produce invalid values. To fix the problem, use a full stop (period) as a decimal separator.
• A limited way to work around invalid input in templates is to use ((digits)), e.g. ((formatnum:((digits|(({votes))))))}. This works only for whole numbers and will produce incorrect results for input containing decimal points or other non-numeric characters.

Ways to fix this error in articles:

• When additional text or references exist in a template parameter that expects only numbers, find a way to move the additional text outside the template or into a different parameter. For example:
  • Currency templates like ((CAD)) or ((US$)) take only numeric input. Use ((US$|123))((nbsp))million instead of ((US$|123 million))
  • The |population_total= parameter in ((Infobox settlement)) should have only a number in it. Move any references to |population_footnotes=, as in this edit.

Other:

• When formatnum is given a negative number written with the proper U+2212 "minus sign" (instead of the commonly used hyphen-minus key that appears on most keyboards), e.g. ((formatnum:−9000000)), it assigns this error category; see T237467. A workaround for this incorrect usage was applied to ((US Census population)), which shows population declines as negative numbers. You should use hyphen-minus within formatnum to avoid this error category and it will output the proper minus sign (see T10327).