Section 12A(3)(h) in The Merchant Shipping (Prevention of Pollution by Oil from Ships) Rules, 2010
(h)"Depth (Ds)" is the moulded depth, in metres, measured at mid-length to the upper deck at side and for the purpose of the application, "upper deck" means the highest deck to which the watertight transverse bulkheads except aft peak bulkheads extend,