[经] depreciation-sum of expected life

yù jì nián xiàn zǒng shù zhé jiù ㄩˋ ㄐㄧˋ ㄋㄧㄢˊ ㄒㄧㄢˋ ㄗㄨㄥˇ ㄕㄨˋ ㄓㄜˊ ㄐㄧㄡˋ