Reference 5110 was introduced in 2000 and remained in production until 2006, giving way to the later reference 5130. The present watch, made in yellow gold has a classic Calatrava case, a guillochè silvered Argentè dial and a rotating ring with 24 city names. This very elegant watch, an icon of the Patek brand, allows the wearer to keep track of both local and home time with the simple click of a button located at the 10 o'clock position. Worldtime wristwatches were invented, like most innovations, out of necessity. With the advent of the industrial age came global trade and world travel and, as a result, there was a need for timekeeping devices that could track time in multiple locations.