(1) From time to time the dollar amount specified in RCW 64.90.360(4) and 64.90.640(2) must change, as provided in subsections (2) and (3) of this section, according to and to the extent of changes in the consumer price index for urban wage earners and clerical workers: United States city average, all items 1967 = 100, compiled by the bureau of labor statistics, United States department of labor, (the "index"). The index for December 1979, which was 230, is the reference base index.

(2) The dollar amounts specified in RCW 64.90.360(4) and 64.90.640(2) and any amount stated in the declaration pursuant to RCW 64.90.360(4) and 64.90.640(2) must change on July 1st of each year if the percentage of change, calculated to the nearest whole percentage point, between the index at the end of the preceding year and the reference base index, is 10 percent or more, but: (a) The portion of the percentage change in the index in excess of a multiple of 10 percent must be disregarded and the dollar amount may only change in multiples of 10 percent of the amount appearing in this chapter on July 1, 2018; (b) the dollar amount must not change if the amount required under this section is that currently in effect pursuant to this chapter as a result of earlier application of this section; and (c) the dollar amount must not be reduced below the amount appearing in this chapter on July 1, 2018.

(3) If the index is revised after December 1979, the percentage of change pursuant to this section must be calculated on the basis of the revised index. If the revision of the index changes the reference base index, a revised reference base index must be determined by multiplying the reference base index then applicable by the rebasing factor furnished by the bureau of labor statistics. If the index is superseded, the index referred to in this section is the one represented by the bureau of labor statistics as reflecting most accurately the changes in the purchasing power of the dollar for consumers.