NOMOS Glashütte Tangente Datum GangreserveNOMOS Glashtte Tangente Datum Gangreserve Reference No.: 131 The design classic enhanced with a black (and patented) power reserve indicator, preventing you from forgetting to wind the watch. The date (another NOMOS patent) reminds you of anniversaries and birthdays. The date ring was wrapped around the movement, while the power reserve mechanism is integrated in the barrel ensuring that the watch remains flat and elegant.