“A way to figure depreciation for certain property. It is determined by estimating the number of units that can be produced before the property is worn out. For example, if it is estimated that a machine will produce 1,000 units before its useful life ends, and it actually produces 100 units in a year, the percentage to figure depreciation for that year is 10% of the machine’s cost less its salvage value.” Pub. 946, How to Depreciate Property (2020), IRS.