Reversal of vat credit

Dear All

We have the latest vat credit amended wherein we need to reverse  vat credit the rule  is  provided below. Can anybody  guide me the logic/formula to be adopted and what is the %  is to be reversed.

1. Amendment of Section 19- Whenever CST sale is made under Section 8(1) of the CST Act, 1956, the proviso to Section 19(2)(v) as amended seeks to restrict the [ITC] input tax credit by providing that credit shall be allowed in excess of 3%. This means that if local purchases attract 5% or 14.5% VAT and the output is sold on CST basis falling under Section 8(1) of the CST Act, the reversal would be to the extent of 3%.

Thanks

S.Hariharan-Chennai