12. (1) For the purpose of verifying the correctness of commercial weights and measures, the Government may cause to be prepared as many sets of standard weights and measures, to be called working standards, as it may consider expedient and shall cause each such set to be authenticated as having been verified with the secondary standards: Working Standards Provided that the working standards in respect of bullion and precious stones shall be verified with the reference standards. (2) The working standards shall be kept in such place and in such condition as may be specified by the authorised persons who shall cause them to be verified with the secondary standards or reference standards, as the case may be, at such intervals and in such manner as may be specified by him and to be marked with the date of such verification. (3) A working standard which has not been verified at any interval specified therefore shall not, after the expiry of the day closing the interval, be used until it has been verified and marked with the date of verification.