"For a father, it's very difficult to teach a son," Stern says. "It's human; it's always like this. The father is not a great teacher. Knowing this, my son had a coach. And I think this was a very good formula. The coach was one of my friends; he knows Patek very well, and it was easier for him to tell certain things to my son than if I had to tell it. This was successful. I was very lucky because my son always wanted to come to Patek, so it was my task to give him the best education so that he could take over."

When Stern was studying the business in the 1960s, he spent several years based at the Patek offices in New York City learning the basics. The people who worked with him at the time expected him to be a bit of a snob, but they remember Stern as a warm man who didn't mind the most menial tasks.

"What impressed us, here he comes over, he's the son of the owner, and he was willing to do anything," says Hank Edelman, who today directs Patek's U.S. operations. "In the '60s, there were ladies' watches made with little suede cords. It was tedious to put them on; you had to insert a wire into the cord and tie it in a certain way so it wouldn't scratch the owner's wrist. That was the style in those days, and we would get shipments from Geneva and sit there and put 40 on at once. It was time-consuming, and no one liked it, but it impressed our team that he did it for hours. He was more than willing."

Edelman says the same process is being repeated with Thierry, who spent time working in the company's New York City mail room while learning the trade from the ground up. Thierry is now vice president of the company, and he's poised to take over when his father decides to step down.