The Nigam shall create a depreciation reserve and, shall at the end of every year, credit to such reserve from its revenue an amount calculated in accordance with the straight line method of depreciation, that is to say, such an amount as is arrived at by dividing ninety per cent of the original cost of the asserts, after taking into account the sums already written off and set aside in the books of the Nigam by the prescribed period in respect of such assets :
Frovided that the contribution in respect of any asset to the depreciation reserve under this Section shall cease at the end of the prescribed period or when the asset cease to be used by the Nigam whichever is earlier:
Provided further that if in any year it is not practicable fully to comply with the provisions of this Section, the amount by which the sums actually credited falls short of the amount required under this Section in respect of that year shall be carried forward and together with simple interest thereon at the Reserve Bank rate ruling at the beginning of that year, shall be credited to the said reserve as soon as it is found possible so to do:
Provided also that the accumulations in the depreciation reserve may be invested in the business of the Nigam or utilized for repayment of the principal of any loan raised under sub-section (1) of Section 20 or for repayment of sums paid by the State Government under sub-section (2) of the said Section.