$1000 is not any legally specific number. Whatever you sell that is not on your depreciation schedule has a current basis of 0 and 100% of your proceeds are ordinary business income.
General assets up to $2500 under safe harbor de minimis can be straight expensed. But you should record them as assets to begin with so you can support the expense (similar to taking 179 expense)
Example you buy a new computer for 2400, you can expense full amount this year and turn around and sell it in two years when it is obsolete to you for 1200 and you record 1200 business sales income
