For the grazing years 1979 through 1985, the Secretaries of Agriculture and Interior shall charge the fee for domestic livestock grazing on the public rangelands which Congress finds represents the economic value of the use of the land to the user, and under which Congress finds fair market value for public grazing equals the $1.23 base established by the 1966 Western Livestock Grazing Survey multiplied by the result of the Forage Value Index (computed annually from data supplied by the Economic Research Service) added to the Combined Index (Beef Cattle Price Index minus the Price Paid Index) and divided by 100: , That the annual increase or decrease in such fee for any given year shall be limited to not more than plus or minus 25 per centum of the previous year’s fee.Provided