The Revenue Act of 1954 permitted entrepreneurs for the first time to make use of the double declining balance (DDB) and sum of the year's digits (SYD) methods of depreciation in place of the customary straight line method (SL). The tax advantages from using such methods are well known.1In spite of these advantages, however, the accelerated methods in many cases appear to have been adopted only slowly over the years. Clearly any attempt to determine the effect on investment of such provisions must rely on knowledge of the extent of their use. Unfortunately there is no direct information available, nor do estimates exist, for the two-digit manufacturing industries on the fraction of investment in each year since 1954 written off by accelerated methods. In this paper an attempt is made simultaneously to estimate such figures on an annual basis and to fit a learning curve to them.2