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THE APERTURE / WINDOW

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1. General description

An “aperture / window” refers to an opening made in the dial through which information is displayed. This information can be of various kinds, such as the date / calendar, the day of the week, the moon phase, or even more complex functions, such as a Dual time zone (GMT) or astronomical indications. Apertures / Windows are often used to complement the dials of complicated watches and make them easier to read.

2. History

Apertures / Windows have their origins in the earliest mechanical timepieces, where additional information was needed to accompany the basic time display, notably as early as the 14^th century, with the first astronomical clocks. Whatever the type of clock or watch concerned, watchmakers have never ceased to make use of them.

3. Functions displayed by aperture / window

Apertures / Windows can be used to display various pieces of information, ranging from the simplest to the most complex functions:

• Date / Calendar: Displaying the date via an aperture is one of the most common functions. It is often integrated in the form of a small circular or rectangular window in the dial, with a rotating disc visible through it.
• Day of the week: This type of display is often combined with the date display and is generally placed in a separate aperture, located at the bottom or top of the main display. In many cases, the day aperture may be displayed in the form of a sector, in order to show the day’s name spelled out in full.
• Moon phase: An aperture for the moon phase is generally wider and may be a rotating disc displaying the different phases of the moon over a 29.5-day cycle. This type of aperture is often located at 6 o’clock on the dial and takes the shape of a crescent.
• Month : As with all calendar information, the month is frequently displayed by a combination of disc and aperture, which improves readability compared to a hand-based system.
• Power reserve indicator: Although it is often a circular counter, some watches have a dedicated aperture / window for displaying the power reserve, which indicates the number of hours remaining before the watch stops. In many cases, a gauge-type display indicates the level of charge of the mainspring.
• Dual time zone (GMT): Dual time zone watches may use an aperture / window to display the time of another time zone, in addition to the main hour and minute display.
• Other information: Most of the information a watch can display can be shown via an aperture / window system. This list is therefore not exhaustive.

4. Shapes and finishes

Apertures / windows are designed to blend harmoniously with the dial, while respecting the watch’s aesthetics and the readability of the display. Several shapes and sizes can be used for apertures / windows, including:

• Rectangular or square: These are the classic shapes for an aperture / window, notably to display the date / calendar or the day of the week. The corners can be rounded or sharper, depending on the design of the watch.
• Circular: Less common, a circular aperture / window can be used. Generally, these are favored for secondary information (leap year cycles, chime active or silent, etc.).
• Sector: In order to display more characters, typically the name of the day of the week, some apertures / windows open in a sector shape.
• Other shapes: For watches with a bolder design or for specific functions, apertures / windows with more specific shapes may be chosen.

To enhance the legibility of the information displayed through the aperture / window, its edges are often given special finishes:

• Beveling / Angling / Diamond polishing : The outline of the apertures is generally framed by a marked bevel, the purpose of which is to improve the readability of the information, bring more light to it and give it a certain elegance. In some cases, this bevel will be diamond-polished (polished)
• Applied markers : The edge of the apertures can be slightly raised by a metal applied marker to accentuate its presence on the dial and improve its readability and brightness.
• Magnifiers: To improve the readability of information printed in small format, some watchmakers install a magnifier directly within the aperture frame.

5. Positions on the dial

The position of the apertures varies according to their function and the overall aesthetics of the watch. The most common positions are:

• At 3 o’clock : This is the traditional location for date apertures / windows. It can be slightly shifted downward or upward to incorporate a day-of-the-week display.
• At 6 o’clock : This is an ideal position for larger apertures / windows, such as those displaying moon phases or power reserve. This position helps balance the dial, especially in watches where the time function already occupies a large part of it.
• At 12 o’clock : Less common, but sometimes used for complications such as an additional time zone display or a big date.
• Asymmetrically scattered : On certain luxury or more complex watch models, apertures / windows can be arranged asymmetrically to add a touch of originality or to better fit with the other dial complications.