Technique → Dial & Display

APERTURE

An aperture in the watch dial displays information that can vary widely, from the date and day of the week to moon phases or more complex functions such as dual time zones or astronomical indications. Apertures are often used to complement the dials of complicated watches, enhancing both functionality and readability.

History

Apertures, of window displays, originated in the earliest mechanical timepieces, where additional information was needed to accompany the basic time display. This practice dates back as early as the 14th century with the advent of astronomical clocks. Regardless of the type of clock or watch, horologists have continuously relied on window displays to enhance functionality.

Functions Displayed by Aperture

Apertures can be used to present a range of information, from simple to highly complex functions:

  • Date: Displaying the date via an aperture is one of the most common functions. Typically integrated as a small circular or rectangular aperture in the dial, it reveals a rotating disc visible through the opening.
  • Day of the Week: Often combined with the date display, this type of window is generally positioned either above or below the main display. In many cases, the day window is styled as a sector to show the full name of the day.
  • Moon Phase: A moon phase window is usually larger and incorporates a rotating disc that depicts the moon’s various phases over a 29.5-day cycle. This type of window is often positioned at 6 o’clock on the dial and features a distinctive crescent shape.
  • Month: Like other calendar information, the month is frequently displayed via a disc-and-window system, prioritising readability over pointer-based systems.
  • Power Reserve Indicator: Although commonly shown as a circular gauge, some watches include a dedicated window to display the power reserve, indicating the remaining hours before the watch stops. In many cases, a gauge-like display shows the level of tension in the mainspring.
  • Dual Time Zone (GMT): Watches with dual time zone functionality may use a window to show the time in another zone, complementing the primary hour and minute display.
  • Other Information: Most data a watch can display can be presented via a window system. This list is therefore not exhaustive.

Shapes and Finishes

Apertures are designed to harmonise with the dial, balancing the watch’s aesthetic appeal with readability. Several shapes and sizes are used, including:

  • Rectangular or Square: These are the classic shapes for apertures, commonly used for date or day-of-the-week displays. The edges may be rounded or angular, depending on the watch design.
  • Circular: Less common, circular windows are typically used for secondary information (e.g., leap year cycles or active/silent chime indicators).
  • Other Shapes: For bolder designs or specific functions, apertures with more unique shapes may be selected.

To enhance the readability of the displayed information, the contours often feature special finishes:

  • Chamfering/Bevelling: The edges of the window are typically framed with a defined chamfer to improve legibility and reflect light, adding elegance. In some cases, these chamfers are polished.
  • Appliqués: The window edges may be slightly raised or bordered with a metallic appliqué to enhance visibility and brightness.
  • Magnifiers: To improve the readability of small printed information, some watchmakers incorporate a magnifier directly into the window frame.

Position on the Dial

The position of apertures varies depending on their function and the overall watch aesthetics. Common placements include:

  • At 3 o’clock: This is the traditional position for date windows, often slightly shifted up or down to accommodate a day-of-the-week display.
  • At 6 o’clock: This position is ideal for larger windows, such as those showing moon phases or power reserves. It balances the dial, particularly in watches where the main time display occupies much of the space.
  • At 12 o’clock: Less common but sometimes used for complications like additional time zones or a large date display.
  • Asymmetrically Distributed: On certain luxury or more complex watches, window displays may be arranged asymmetrically to add a touch of originality or to better integrate with other dial complications.