There are two ways to tell if the timing belt has been replaced. One is obvious-you are looking at a service receipt showing the replacement.
Swimlane diagrams are used whenever you need to show activities, tasks, or process steps which are being performed by different actors/roles. You can use swimlanes to group activities in an activity diagram or process flow by any category what you need: by role, by system, by department, etc.
Swim to the Interval. Swim to the Interval is a general way of specifying that the swimmer pace himself through a swim such that he doesn't go too fast (getting too much rest) or too slow (getting too little rest).