1. when the first of two boats reaches the zone,
   1. if the boats are overlapped, the outside boat shall at that moment give the inside boat mark-room; WS Case 12
   2. If the boats are not overlapped, the boat that has not reached the zone at that moment shall give the other boat mark-room. WS Case 2 WS Case 12 WS Case 15 WS Case 25 WS Case 59 WS Case 63 WS Case 75 WS Case 81 WS Case 95 WS Case 114 WS Case 118
   When a boat is required to give mark-room by this rule, she shall continue to do so for as long as this rule applies, even if later an overlap is broken or a new overlap begins.
2. Rule 18.2(a) no longer applies if the boat entitled to mark-room passes head to wind or leaves the zone.
3. When rule 18.2(a) does not apply and the boats are overlapped, the outside boat shall give the inside boat mark-room.
4. If a boat obtained an inside overlap from clear astern or by tacking to windward of the other boat and, from the time the overlap began, the outside boat has neen unable to give mark-room, rules 18.2(a) and 18.2(c) do not apply between them.
5. If there is reasonable doubt that a boat obtained of broke an overlap in time, it shall be presumed that she did not