Do please try the search facility or google - anyway - this is one title that came up within the last 6 months to help you out - click on this link:
Educate me. Whats the difference between a Sea Dweller and a Sub
All the best - oh - if you can afford it, the Seadweller 4000 is best in my humble opinion - though the Submariner wears a little slimmer if you don't want the date function.
Martyn.