Section 50 of the Principal Act is amended by inserting "(1)" before "If", by substituting in subsection (1) "shall, subject to subsection (2), be an amount" for "shall be an amount" and by inserting the following after subsection (1):

"(2) An adjustment shall be made so that the amount arrived at by such means to be the property’s net annual value is (insofar as is reasonably practicable and in accordance with section 19(5) or 49, as appropriate) determined by reference to the values of other properties comparable to that property as appearing on the valuation list.".