In this subchapter:
(1) "Consumer price index" means the Consumer Price Index for Urban Wage Earners and Clerical Workers: U.S. City Average, All Items, 1967=100, compiled by the Bureau of Labor Statistics, United States Department of Labor, or, if that index is canceled or superseded, the index chosen by the Bureau of Labor Statistics as most accurately reflecting the changes in the purchasing power of the dollar for consumers.
(2) "Reference base index" means the consumer price index for December 1967.