Section 15 in The Standards of Weights and Measures (General) Rules, 1987
15. Provisions relating to existing weights and measures
.-Any weight or measure which confirms to the specifications laid down by or under any State or Central law shall, if such specifications are in force at the commencement of these rules, continue to be regarded as standard weight or measure for a period of three years from such commencement notwithstanding that such weight or measure does not conform to the specifications laid down in the First to Ninth Schedule (both inclusive) to these rules and every such weight or measure shall be so modified during the period of three years aforesaid as to make them conform to the specifications laid down in these rules:Provided that if the Director is satisfied that the period beyond three years is necessary for carrying out the modification in such weight or measure, he may extend the period for such further period, not exceeding one year, as he may think fit.
