On December 5, 2002 the Federal Reserve published a revision to Industrial Production. The revised estimates will be classified according to the 2002 North American Industrial Classification System (NAICS), previously, the estimates were classified according the the 1987 Standard Industrial Classification (SIC) system. Capacity utilization is calculated for the manufacturing, mining, and electric and gas utilities industries. For a given industry, the utilization rate is equal to an output index divided by a capacity index. Output is measured by seasonally adjusted indexes of industrial production. The capactiy indexes attempt to capture the concept of sustainable practical capacity, which is defined as the greatest level of output that a plant can maintain within the framework of a realistic work schedule, taking account of normal downtime, and assuming sufficient availability of inputs to operate the machinery and equipment in place. History is stored independently for monthly and quarterly frequencies. HP values for these frequencies may not match each other. Note that when only one frequency is stored in history, for the other frequencies, history is derived from that of the stored frequency. For example, HP W, HP M, HP Q and HP Y will derive data from HP D when only daily history is stored, HP Q and HP Y will derive data from HP M when only monthly history is stored. As another example, if both daily and monthly are stored, HP W will derive data from HP D, while HP Q and HP Y will derive data from HP M and so on.