Blog: The Date Window

Date: 16 August 2019

Copyright © David Boettcher 2005 - 2023 all rights reserved.

I make additions and corrections to this web site frequently, but because they are buried somewhere on one of the pages the changes are not very noticeable, so I decided to create this blog section to highlight new material. Here below you will find part of one of the pages that I have either changed or added to significantly.

The section below is from my page about Dials and Hands.

If you have any questions or comments, please don't hesitate to contact me via my Contact Me page.

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The Date Window

Who invented the date window, the little window on a wristwatch dial that shows today's date?

I am pretty sure that Rolex would like us to think that it was them. Today the Rolex web site (accessed 15 August 2019) says “The year 1945 saw the birth of the Datejust, the first self‑winding wrist chronometer to indicate the date in a window on the dial.” This is not quite the same as saying that Rolex invented the date window in 1945, but without the qualification “self‑winding wrist chronometer”, which I am sure that many people would see as just a fancy way of saying wristwatch, it would say that the Datejust was the first watch with a date window.

Rolex did invent the “cyclops”, the magnifier in the crystal that magnifies the date to make it easier to read. This is said to have been inspired by Betty, Wilsdorf's second wife, who complained that the date on her ladies' Rolex wristwatch was too small to read. The cyclops was introduced in the early 1950s.

However, Rolex did not invent the date window itself.

Jean-Louis Jeanmaire

The earliest patent yet seen for a date window is illustrated by the figure from a Swiss patent reproduced here.

It is Swiss patent No. 5139, dated 19 June 1892. The patent was granted to Jean-Louis Jeanmaire, of Orvin near to Bienne. It is titled Quantième à guichet pour montres et pendules or Calendar window for watches and clocks.

The diagrams in the figure illustrate the method of operation.

The date is displayed through a hole in the dial by two circular discs, one numbered 0 to 3 and the other 0 to 9 to allow the full range of dates from 01 to 31 to be displayed. The day of the week is displayed by a third disc through a second hole in the dial below the centre.

The day of the week and the 0 to 9 disc are moved forward by the watch mechanism every twenty four hours. As the 0 to 9 disc completes its revolution, which takes place every 10 days, the index labelled d between the 0 and 9 on its periphery moves to 0 to 3 disc on one place.

The indexing of the date discs would allow 32, 33 etc to appear after 31, but the patent mentions that there are three pushers that enable the discs to be moved at will to any desired position, so presumably the owner of the watch was expected to change the date from 32 to 01.

The separation of the first and second digits of the date onto separate rings is reminiscent of the big date display introduced by A. Lange & Söhne at its relaunch in the Lange 1. Indeed, the patent granted to Jeanmaire says that the two disc construction allows it to be applied to ‘un quantième de très grandes dimensions’, a date of very large dimensions. Lange are careful to say that theirs is the first example of a big date display being used in a wristwatch.

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Marlys' Date Watch

The advertisement from the Watchmaker & Jeweller, Silversmith & Optician for October 1930 clearly shows a wristwatch with a date window; a “Marlys Date Watch” in fact.

In small print the advert says “Patents applied for in all principal countries.”

The fact that the Marly's advertisement says "Now - Marlys gives the date ..." suggests that they thought this was the first wristwatch with a date window. They were granted Swiss and French patents, but although an application was made for a British patent, it was never granted.

• Fabrique d'Horlogerie Marlys S. A. of La Chaux-de-Fonds was granted on 15 December 1931 a Swiss patent for “Mécanisme indiquant le quantième du mois pour montres et pendulettes” or mechanism indicating the date of the month for watches and clocks, the priority date being 16 July 1930.

• The same device was granted a French patent under the title “Mouvement d'horlogerie à quantième”

• An application for a British patent under the title “Date indicating mechanism for watches and small pendulum clocks” was also lodged, but this was allowed to become void.

Marlys seem to have been particularly interested in dials. A patent was granted to them in 1928 for “Instrument permettant de reconnaître si un tour d'heure est correctement placé sur son cadran” or an instrument to recognize if a time lapse is correctly placed on the dial. This was a device for checking that dials were laid out and divided correctly. The purpose was for dial makers to be able to see if a dial printing machine was working properly, or by watch manufacturers to check that dials sent to them were free from defects.

Marlys appear to have been an assembler of watches. Movements of Marlys watches are marked “FEF” for Fabrique d'Ébauches de Fleurier.

The British agency for Marly's was taken by Adie Brothers who then traded under the style “Adie-Marlys Watch Company” at Craven House, 121 Kingsway, London.

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Graef & Co Kalenderuhr

Jon Hallet discovered an application for a British patent with a very similar mechanism, "A watch or clock with a device for indicating the day of the month". This mechanism, called a “Kalenderuhr” was invented by the Swiss company Graef & Co of La Chaux-de-Fonds. The application priority date was 31 January 1930 and it was granted Swiss patent No 148818 on 15 August 1931.

The British rights to this patent were assigned to Claude Lyons of the Vertex Watch Company who made an application for a British patent. This was given the provisional number 377,953, but no patent was granted and the application, like the Marlys application for a British patent, became void. However, the priority date is nearly six months earlier than the Marlys' patents, so at the moment this Kalenderuhr date window is the earliest known.

Unlike the Marlys design, which has the date window below the 12, the Graef & Co Kalenderuhr design placed the date window at the now-familiar position of 3 o'clock on the dial.

Patek Philippe

In the Patek Philippe museum there is a perpetual calendar pocket watch with the date in an aperture at 10 o'clock, and also the day of the week and the month shown through other apertures in the dial.

This watch dates 1928-1929, just a little bit before the Graef & Co Kalenderuhr patent.