Nomos Delta (δ) is a manual winding movement with date display and a power reserve indicator. It is an evolution of the predecessor Nomos 1 TSDPG and was produced from 2005 until 2016 before being replaced by DUW 4401.
The 2005 introduction of the Alpha movement family was an important turning point for Nomos. Although based on the preceding Nomos 1 TSP, it was largely constructed in-house rather than being a refinished ebauche. The gear train is similar to the classic Peseux 7001, but was placed in a new enclosure based on the classic Glashütte three-quarter plate design. Nomos updated many of the components, adding hacking seconds, and completely reworked the finishing with rhodium-plated surfaces, blued screws, Glashütte Stripes, and Glashütte solar grinding or Langeleist-Perlage.
Calibre Delta (with date and power reserve indicator) was released at the same time as Nomos Alpha (without date) and Nomos Beta (with date). All three are hand-winding movements, as was the Nomos Gamma which followed in 2007. In 2006, Nomos followed with a family of automatic movements, Epsilon, Zeta, and Xi, with similar features. Alpha is smaller than the others, however, at just 23.3 mm diameter and 2.6 mm thick.
The Beta and Delta movement adds an unusual and patented date display. Typically, a date wheel and associated gears are stacked below the mainplate between the rest of the watch movement and the dial. However, this makes these movements more bulky and thick. Instead, Nomos places the date ring around the movement, with the switching mechanism integrated into the movement itself, making the Beta and Delta nearly as thin as the Alpha, on which they are based. The power reserve indicator is also integrated into the bottom plate of the movement, adding no additional thickness. It shows the remaining power in the mainspring, serving as a reminder to wind the watch.
For the Tangente Observatory, the date index is modified to function as a day/night display.
This movement is officially named using the Greek letter “δ”, but Nomos often writes it as “Delta”.
This movement is part of a family of Nomos movements produced since 2005. The movement is partially made in-house, though the assortment is supplied by a third-party. It was supplanted by the in-house Nomos Swing System family starting in 2014.