Section 12(4) in The Merchant shipping (Radio Direction Finders) Rules, 1968.
(4)The Master of every ship shall cause the calibration tables and curves prepared in accordance with the foregoing provisions of this rule to be verified by means of check-bearings"(a)at intervals not exceeding twelve months; and(b)whenever any change is made in any structure or fitting on deck which is likely to affect the "accuracy of the radio direction-finder.If such verification shows that the calibration tables or curves are materially inaccurate, the Master of the ship shall cause the radio direction-finder to be recalibrated as soon as practicable in the manner specified in sub-rules (2) and (3).
