15.—(1) The attained subdivision index of every ship shall not be less than the required subdivision index of that ship.
(2) The attained subdivision index of a ship is the value “A” calculated in respect of that ship in accordance with the formula specified in paragraph 3 of Annex I in Merchant Shipping Notice No. M.1476 and the required subdivision index for a ship is the value “R” calculated in respect of that ship in accordance with the formula specified in paragraph 2 of Annex I to that Notice.
(3) In calculating “A” and “R” account shall be taken of the explanatory notes set out in Annex II to that Merchant Shipping Notice.