Section 19 in The Standards of Weights and Measures (National Standards) Rules, 1988
19. Period and manner of verification of reference, secondary and working standards
(1);Every reference standard shall be verified and certified in terms of the National Standards by the National Physical Laboratory, at an interval not exceeding three years:Provided that in the case of length measures such interval shall not exceed five years.(2);Every secondary standard shall be verified against the appropriate reference standard by the Reference Standard Laboratory, at an interval not exceeding two years.(3);Every working standard shall be verified against the appropriate secondary standard, by any of the laboratories where secondary standards are maintained, at an interval not exceeding one year.
