See https://www.irs.gov/publications/p946#en_US_2019_publink1000107576
When using a declining balance method, you apply the same depreciation rate each year to the adjusted basis of your property. You must use the applicable convention for the first tax year and you must switch to the straight line method beginning in the first year for which it will give an equal or greater deduction. The straight line method is explained later.
