How is a FOB primarily used in watch design?

In watch design, a FOB is primarily used to decorate and secure a watch. It serves as a decorative element that adds aesthetic appeal to the timepiece while also providing a functional purpose, often allowing the watch to be attached to a chain or a pocket, especially in pocket watches. This combination of securing the watch and enhancing its visual design is crucial in crafting a distinctive product that appeals to consumers.

The other options, while relevant to various watch features, do not accurately represent the primary function of a FOB. For instance, enhancing water resistance is typically achieved through different materials and design techniques rather than through the FOB itself. Similarly, measures to improve time accuracy stem from the movement and mechanics within the watch, rather than the FOB's role. Providing multiple display options is generally associated with the design of the watch face and functionality rather than a component meant for decoration and security.