Section 69.13 - Applying provisions of a measurement system(a) Except as noted under paragraph (c) of this section, all provisions of a measurement system as prescribed in this part that are applicable to the vessel must be observed. Coast Guard interpretations of these provisions are published by, and may be obtained from, Commanding Officer, Marine Safety Center (MSC-4).(b) The provisions of more than one measurement system must not be applied interchangeably or combined, except where specifically authorized under this part.(c) Unless otherwise provided for by law, the tonnage measurement rules and procedures that immediately predate the rules and procedures prescribed in this part may be applied, at the option of the vessel owner, to the following vessels:(1) A vessel which has not been measured and which was contracted for on or before May 2, 2016.(2) A vessel which has been measured, but which has undergone modifications contracted for on or before May 2, 2016.USCG-2011-0522, 81 FR 18719 , Mar. 31, 2016 USCG-2011-0522, 81 FR 18719, 3/31/2016