Tax deductions for depreciation have been allowed in the U.S. since the inception of the income tax. Prior to 1971, these deductions could be computed in a variety of manners over a wide range of lives, under old Bulletin F. In 1971, Congress introduced the Class Life Asset Depreciation Range (ADR) system in an attempt to simplify calculations and provide some uniformity. Under ADR, the IRS prescribed lives for classes of assets based on the nature or use of the asset. Such classes included general classes (such as office equipment) and industry classes (such as assets used in the manufacture of rubber goods). Taxpayers could use their choice of several methods of depreciating assets, including straight line, declining balance, and sum of years digits. Asset costs and accumulated depreciation were tracked by "vintage accounts" consisting of all assets within a class acquired in a particular tax year. All vintage accounts for the same year were assumed placed in service in the middle of the year; however, a taxpayer could elect the modified half year convention with potentially favorable results.