IWC produced the first “digital” watches in its history as early as 1884. These timepieces, known as Pallweber watches, displayed the hours and minutes using numerals, while the seconds were shown in analogue form with a hand. In 2009, IWC unveiled a surprise for watch lovers in the form of a newly developed perpetual calendar movement, which shows not only the date but also the month in large numerals. In 2013, the year of the Ingenieur, tinted glass inlays on the dial of the Ingenieur Perpetual Calendar Digital Date-Month provide a view of the discs at work. The energy required to advance the month display discs is built up continuously throughout the month by a quick-action switch. A spring-loaded lever on the quick-action switch is lifted a tiny bit further each day by a cam. At the end of the month, the tension in the spring has reached its maximum, and it is time for all that energy to be released; the quick-action switch jumps instantaneously to its starting position and advances both of the month display discs individually, or together, by one position, depending on the month. On 31 December, the leap year disc is also advanced at the same time.