A unique partnership in retailing was celebrated in July by Patek Philippe, one of the world’s premiere watchmakers, and by Tiffany & Co., one of the world’s leading luxury goods retailers. That business relationship began with a handshake agreement in 1851 between company founders Antoine Norbert de Patek and Charles Lewis Tiffany.

Officials of the two firms marked the 150th anniversary of that agreement with a new limited-edition 18k timepiece called “T 150,” the first watch made by Patek Philippe for an American retailer. It was created in the company’s workshops in Geneva, Switzerland, under the guidance of company president Philippe Stern and his son Thierry Stern. Sales of the T 150 began this fall in Tiffany & Co. stores.

The limited-edition watch “celebrates the dedication to excellence that is the foundation of both companies, our partnership, and our mutual success,” says Michael J. Kowalski, Tiffany president and chief executive officer. “[It] is symbolic of the vision [we] have shared for 150 years and will continue to share.”

Only 450 watches will be made—150 in yellow gold for $21,000, and 150 in rose gold and 150 in white gold for $22,500 each.

The timepiece “is a unique expression of Patek Philippe’s unparalleled relationship with Tiffany & Co.,” says Philippe Stern. Its design not only “touches us in a very personal way but also gives the collector something truly rare and valuable.” The watch’s design features the distinctive Tiffany “T” at 12 o’clock and the names of both companies on the dial—the first time Patek Philippe has allowed a retailer’s name to appear on a dial. The T 150 is based on the watchmaker’s patented Annual Calendar watch; uses rectangular windows for month, date, and day displays (popular on watches made for the U.S. market in the 1930s and ’40s); and, for the first time, numerals as month indicators. An engraving of the original Patek Philippe store in Geneva appears on the caseback, with names of both companies on the façade and the dates “1851-2001.”