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@ptax255 wrote:

method of accounting for inventory

treats inventory as non-incidental material or supplies,

or conforms to your financial accounting treatment of inventories

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Is this their first year?  If not, you need to follow their prior "method of accounting".

If this is their first year, one of the options is to "conforms to your financial accounting treatment", which could be deducting the full cost in the year of purchase (something that was added somewhere around the Tax Cuts and Jobs Act).