For age and service annuity, the minimum annuities prescribed in Sections 6-123 and 6-128 and for disability benefits, salary as defined in Section 6-111 shall be the basis of computation. For disability pension and duty disability benefit under this Article, it shall be assumed that the annual salary of a fireman is the amount set out and appropriated for the rank or grade held by him in the annual budget or appropriation of the city, and that when salary is appropriated in a lump sum to be paid on the basis of a daily wage for services as needed, the annual salary is the amount ascertained by multiplying the daily wage by 280; provided that (1) for computing minimum annuity, disability pension and duty disability benefits from and after January 1, 1941, the salary shall be assumed to be not less than the salary appropriated for the rank or grade held by the fireman concerned on December 31, 1940; and that (2) when the amount of salary appropriated for a position is for a definite period of less than 12 months in any one year subsequent to December 31, 1940, disability benefit shall be computed upon the basis of a daily wage or salary by dividing the amount appropriated for such disabled person by 365; and (3) the amount of duty disability benefit, either in itself or when added to child’s disability benefit, shall not exceed the actual salary appropriated for the rank or grade held by the disabled person when the right to such disability benefits accrues.
     The provisions of this section shall be retroactive to January 1, 1941, but shall not apply to any person whose pension, annuity or disability benefit has been or shall be granted, based upon or computed in accordance with the provisions of any Act other than this Article or the “Firemen’s Annuity and Benefit Fund of the Illinois Municipal Code”.