Abstract: An accessory includes a body including a dial having a surface and multiple sets of optically-recognizable identification marks formed as part of the surface. The identification marks for each set are formed to be recognizable by a sensor having a two dimensional array of pixels. An apparatus includes a body comprising a groove having a first surface configured to align with a second surface of an accessory when a portion of the accessory is placed into the groove and a sensor formed in the first surface. The sensor includes a two dimensional array of pixels. An apparatus captures, with the sensor, an image of one of a set of multiple optically-recognizable identification marks formed as part of a surface of the dial, determines from the captured image a specific one of multiple possible accessories interchangeable for use with the apparatus, and performs configuration operation(s) based on the specific accessory.