Patek Philippe

Newbie here, can anyone tell me what model is this Patek? And how come when I pull the crown to set the time, the seconds hand still moves (As opposed to my other watches..) Thanks!...  

I bought this watch from A..., where the picture is from. I hope they don't mind me using it. The description is as follows: Patek Philippe, Genève, Ref. 3734/2. Made in the 1970s. Fine, "carré galbé", center-seconds, self-winding, water-resistant, 18K ye...