In this Act, unless the context otherwise requires,-

(40) "Turnover of sales", in relation to any period, means the aggregate of the sale-prices or parts of sale-prices receivable by a dealer, or if a dealer so elects, actually received by the dealer, during such period after deducting therefrom-

(a) the sale prices or the parts of sale-prices, if any, in respect of sale during such period of, goods specified in Schedule IV other than rice, wheat, foreign liquor and country liquor as specified in that Schedule, which are shown to the satisfaction of the Commissioner to have been purchased by the dealer in West Bengal, but excluding such sales as the State Government may, by Notification, specify

(b) the amounts, if any, refunded by the dealer in respect of any goods returned by the purchaser within such period, and

(c) the amounts, charged as surcharge payable under section 16 and the amounts charged as additional surcharge payable under Section 16A and the amounts charged as turnover tax payable under Section 16B during such period:

PROVIDED that an election as aforesaid once made shall not be altered except with the permission of the Commissioner and on such terms and conditions as he may think fit to impose;