A rotatable disc comprises a first zone in which a plurality of features, e.g. optical filters, are located at uniform angles from each other with respect to an axis of rotation of the disc and a second annular zone comprising sets of adjacent marks of a first type and of a second type. Each set may have a same total circumferential length, but the marks of a given type may have at least two different total circumferential lengths within a set of marks, or may be distinguishable by the relative position of marks of the different type to each other. The adjacent marks of the first and the second type may also form a code pattern that can be used for identifying the features. A method for adjusting the rotational orientation of the disc based on detecting the widths of the sectors is described.