It's a simple piece of arithmetic. Take a company that produces 10,000 watches a year. If success is on the cards, after twenty years it will have sold 200,000 watches to customers at the four corners of the globe (Fine Watchmaking being an international market). Of these, the company can expect an annual return rate of around 10%, ranging from vintage pieces to watches suffering from stopped mechanisms, manufacturing defects, misuse or simply in need of a service. Add two and two together and some 20,000 watches will be making their way to the company's after-sales service door: twice annual production.