An assembly for indicating the angular position of a rotary mechanism (e.g. a valve) with which the assembly is operatively connected has inner and outer cylinders which can be rotated relative to each other. The curved surfaces (20, 35) of the cylinders have areas (25 - 27) of contrasting colour so as to provide different visual effects depending on their relative positions. The areas extend axially and circumferentially and each at least in part decreases axially as it extends circumferentially so that even if part of the outer surface of the outer cylinder is obscured from sight the visual effect and thus the angular position can be observed. The areas may be helices. The surfaces could be conical. Various combinations of colour and area are described. <IMAGE>
