Patek Philippe

Hi, everyone. I've recently come into possession of a ladies Patek Philippe 3313/2 with the original papers. I don't really know much about it, and I haven't been able to find any information on the internet about this particular model. Does anyone know a...  

one of these was sold on a well known auction site in 2000. Paraphrased from that site is the following information (not sure I am allowed to post the link or copy the info): Produced 1950s 18K white gold & diamonds Details of case, dial, and movement on ... 

Thanks very much! I see that the price it went for is listed as 10,500 CHF "including buyer's premium." What does that premium refer to, and how much of that price would it be?