An input mechanism for a portable electronic device includes a rotational manipulation mechanism, such as a cap or shaft. The input mechanism also includes a sensor having first capacitive elements coupled to the manipulation mechanism, second capacitive elements, and a dielectric positioned between the first and second capacitive elements. Movement of the manipulation mechanism alters the positions of the first and second capacitive elements with respect to each other and is determinable based on capacitance changes resulting therefrom. In some implementations, the second capacitive elements may be part of an inner ring or partial ring nested at least partially within an outer ring or partial ring.