Located in the carriage of the watch, the perpetual calendar which measures a mere 1.7 mm thick, is programmed to take automatic account of the different length of each month up to the end of February 2100. Thus, for example, the date shown after 28 February 2007 will automatically be 1 March. But on 1 January 2036, a white letter B on a red background will appear, signalling that it is a leap year in which the month of February will have 29 days. The calendar then jumps two non-existent dates: 30 and 31 February. At the end of each month, the digital date indication must display its exceptional jumping abilities by returning to its departure point, meaning number 1, in under a tenth of a second so that the days of the month can start their round again. This disc designed for this purpose is made from sapphire. It always stops at exactly the right place and never shifts along its axis, since the following month might otherwise end up beginning with the 2nd or the 3rd.