annual calendar

description by ludwig oechslin

task / idea

a watch featuring an analogue display and an ultra simple calendar mechanism that needs manual adjustment just once a year.

solution / implementation

the calendar can be displayed using 50 perforations. 31 for the date, 12 for the months and 7 for the weekdays. in my solution, the conventional date disk mechanism provided by the movement drives the disk bearing the date dot, which rotates beneath the dial with its 31 perforations. the colored dot on the date disk moves from day to day. if you supplement the date disk with a set of teeth and a position ring to the inside, these teeth can perform the function of a maltese cross gear, which, as it moves, drives the month indication cog via an intermediate wheel. the month indication cog, in turn, is equipped with long and short teeth, whereby the long ones are arranged in such a way as to engage, on the 31st of the month, with a tooth on the hour wheel and, via this, provide a further impulse of one day at the end of a month with 30 days, in order to provide an impulse to the 1st of the following month immediately after the impulse to the 31st. the impulse passed on to the month wheel is transferred from the latter via its intermediate wheel to the date disk. this arrangement of wheels allows me to transform the movement’s simple date calendar function into a semi-perpetual annual calendar, i.e. one that needs adjusting just once a year at the end of february. the weekday disk also receives an impulse from the finger located in the middle of the hour wheel, such that a maltese cross is formed. the impulse is received twice a day. to compensate for this, the weekday is displayed by means of a broad colored dot visible through the circle of seven perforations. this colored dot is arranged in such a way that it appears in two perforations between 6 o’clock in the evening and 6 o’clock in the morning to indicate the expiry of the current day and the approach of the following one; between 6 o’clock in the morning and 6 o’clock in the evening, the user sees only the dot indicating the current day. this reflects the 24-hour display by indicating midnight when the user is adjusting the calendar date.