22. Calculation of input tax credit.  Subject to the provisions of rules 23 and 24, a taxable person shall be entitled for input tax credit of whole of the amount of tax paid on purchases of goods during the tax period or return period after reducing there from the reverse in put tax credit if any: Provided that in respect of the goods, specified in sub-sections (2) and (3) of section 13 of the Act, the input tax credit shall be availed only to the extent by which the amount of tax paid in the State exceeds four percent: Provided further that the purchase tax paid under section 19 of the Act, shall be considered as input tax credit for the purpose of subsequent sale in the hands of same person. Provided further that where a person has purchased goods for further use in manufacture of taxable goods including certain products or by-products, which are tax free, then the input tax credit available on the purchase of such goods shall be reduced in proportion of the value of the tax free goods produced to the total value of goods produced.