67. (1) Where, an assessee who is required to pay advance tax under section 64 estimates, at any time before the last instalment is due, that the tax payable by him for the relevant assessment year is likely to be less than the amount of tax as computed under section 65, he may, after giving to the Deputy Commissioner of Taxes an estimate of the tax payable by him, pay such estimated amount of advance tax, as reduced by the amount, if any, already paid, in equal instalments on the due dates of payment under section 66. (2) The assessee may furnish a revised estimate of such amount at any time before any of such instalments become payable and may thereby adjust any excess or deficiency, by reference to the amount already paid by him under this section, in any subsequent instalment or instalments payable in such financial year.