The sub-dials on a chronograph watch are usually fixed and not customizable. These sub-dials are designed with specific functions related to a chronograph, such as measuring elapsed time, recording seconds, minutes, or hours. Manufacturers carefully engineer these sub-dials to provide precise timing and to align with the overall design of the watch. While some high-end or specialized watches may offer limited customization options, standard chronograph watches typically have fixed sub-dials that cannot be altered or personalized by the user.