Rolex introduced the Yachmaster II a few years ago and to date it is the biggest Rolex ever made at 43mm. The Yacht-Master II has a specially designed movement that can be programmed to start between 1 and 10 minutes to accommodate sailing regattas that have varying start sequences.
According to Rolex "The Yacht-Master II is equipped with a Ring Command bezel designed and developed by Rolex, Rotatable 90 degrees, this innovation allows access to the programming funtion of the countdown, then to the locking of this programming. Although is is very complex from a watchmaking point of view, this interaction between the bezel and the movment makes the Yacht-Master II extremely easy to use."
Rolex has a special site dedicated to the Yachmaster II that starts out with a great sailing film which you can visit by clicking here.
Rolex also has a site where you can not only about learn how the Yacht-Master II functions, but Rolex has a really cool interactive online demo that allows you to play with programming the Yacht-Master which you can visit by clicking here.
There is a downloadable users guide for the Yacht-Master II that includes an interactive demo that allows you to play with programing the Yacht-Master. There is a Mac and PC version available here.