Complications  /  Date

Date

Also known as — Quantieme simple, date window

A ring of thirty-one numerals advanced once every twenty-four hours, read through an aperture or by a pointer.

How it works

The date is the most frequently consulted piece of calendar information in ordinary life, and until the middle of the twentieth century anyone who wanted it consulted a diary, a newspaper or a colleague. It is nearly free to a watch, which already counts days. What delayed it was space: the date ring and its indexing works occupy the outer margin of the movement, which in a small wristwatch calibre was already crowded.

hourwheelone turn / 12 h2:124-hourwheelfingerone turn / 24 hone tooth14jumper holdseach numeral squaredate ring, 31 teeth21:0003:00do not force the quickset here
The watch already counts days: the hour wheel turns twice in twenty-four hours. Halve that, hang a finger on it, and once a day it pushes the date ring on by one tooth.

The drive is a chain of reductions. The hour wheel turns once in twelve hours and drives an intermediate wheel geared two to one, so that wheel turns once in twenty-four. It carries a finger which, at each revolution, engages one tooth of the date ring; a sprung jumper bearing on the teeth holds each numeral square in the aperture. In the commonest arrangement the finger tensions the jumper until it passes the crest of a tooth and snaps the ring forward. An instantaneous calendar instead stores energy through the evening in a separate cam and releases it in a fraction of a second at midnight, at the cost of a sudden demand on the mainspring.

The mechanism puts an obligation on the wearer: five corrections a year, and three days after a common February. The chain of reductions also creates the danger zone. For roughly the hours between nine in the evening and three in the morning the finger is engaged with the date ring, and forcing a quickset then can bend the finger or break a tooth.

Recorded here

Milestones with this mechanism

1945The first automatic chronometer with dateRolex’s Datejust of 1945 was the first self-winding, waterproof, chronometer-certified wristwatch with a date in a window.Rolex1956The first day-date wristwatchThe Rolex Day-Date of 1956 was the first wristwatch to show the day spelled out in full and the date, each in its own window.Rolex1969The first high-beat chronographZenith’s El Primero, calibre 3019 PHC, was the first chronograph to run at 36,000 vibrations an hour, fine enough to time a tenth of a second.Zenith1969The first automatic chronograph soldSeiko’s calibre 6139 was the first self-winding chronograph to go on sale, in Japan in May 1969.Seiko1969The first modular automatic chronographHeuer, Breitling, Hamilton-Büren and Dubois Dépraz built Calibre 11 by adding a chronograph module to a thin self-winding movement.Heuer1969The first quartz wristwatchSeiko sold the first quartz wristwatch, the Quartz Astron, in Tokyo on 25 December 1969.Seiko