问题如下：
At the beginning of 2009, Glass Manufacturing purchased a new machine for its assembly line at a cost of $600,000. The machine has an estimated useful life of 10 years and estimated residual value of $50,000. How much depreciation would Glass take in 2009 for financial reporting purposes under the double-declining balance method?
选项：
A. $60,000.
B. $110,000.
C. $120,000.
解释：
C is correct.
Double-declining balance depreciation would be $600,000 × 20 percent (twice the straight-line rate). The residual value is not subtracted from the initial book value to calculate depreciation. However, the book value (carrying amount) of the asset will not be reduced below the estimated residual value.
解析：加速折旧法折旧费用=（2/使用年限）*年初固定资产账面净值=（2/10）*$600,000=$120,000。
请问双倍余额递减法怎么判断折到了最后一期呢？学完忘记了
