The Rolex Cosmograph Daytona has one large dial on the face with three smaller subdials
Dial, Face, and Subdial
Most watches feature a dial that takes up most of the face, and these terms are often used interchangeably. However, the face refers to the entire area exposed to view at the top of the watch, while the dial is only the area used to orient the hands. Many watches also feature sub-dials for timekeeping, small seconds, or other complications. Many modern designs feature overlapping dials, skeletonization, digital counters, inset dials, and other design elements which expose or obscure the face or dial.
Most dials are decorated with markers, numerals, lettering, and so on. This ring of numerals or markers is often called a chapter ring, though those that resemble a railroad are called a track. Dials that emphasize four quadrants are called crosshair dials, and those with crosshair and track are sector dials. Many dials are decorated using guillochage in patterns and textures.
Some watches have additional smaller dials for small seconds or complications known as subdials. These usually have their own chapter ring but usually have simpler decoration due to their size and function. A few special watches, such as the Jaeger-LeCoultre Reverso Duoface have multiple main dials and subdials.
Jaquet Droz leaves much of the face open, with smaller inset dials
© Jaquet Droz
The face of the watch is sometimes taken up by a single large dial but many designs use it in other ways. Jaquet Droz typically uses overlapping subdials for hour/minute and small seconds, and regulator watches usually have three or more smaller dials, each with a single hand for one timekeeping function.
Watches with an opening in the face through which the movement (especially the escapement) can be viewed are called open heart or openworked, while watches with broader open surfaces are called skeleton.