(1) Adjustment shall be made for inflation for the purpose of paragraph (c) of section 21 of the Act by calculating interest on the value of the construction work as estimated for the purposes of paragraph (a) or (b) of section 21 of the Act at the CPI rate as determined by the Board in accordance with subregulation (2).

(2) The CPI rate of interest to be used under subregulation (1) shall be determined by the Board in accordance with the following ¾

(a) in this subregulation }Index~ means the table described as the Consumer Price Index Numbers (All Groups Index) for Perth published by the Commonwealth Statistician under the Census and Statistics Act 1905 of the Commonwealth;

(b) the CPI rate shall be determined before 1 July to take effect for the following year from 1 July to 30 June;

(c) the percentage rate determined under paragraph (b) shall be that which the Board declares to be the percentage by which the Index for the quarter ending in March of the current year is greater than the Index for the quarter ending in March of the previous year; and

(d) if the Index for the quarter ending in March of the current year is not greater than the Index for the quarter ending in March of the previous year, the CPI rate for the following year from 1 July shall be nil.