Abstract: At least one cylinder driven at a constant speed is contained in a casing and a dial plate mounted on the casing is provided with a window extending in the direction of the cylinder. The upper edge of the window is marked with digits. The outer periphery of the cylinder is divided into two sections by a line inclined a definite angle with respect to the axis of the cylinder, and the two areas are coloured by different colours. The inclined line cooperates with the digits to display time. When two or three cylinders are used it is possible to display hours, minutes and seconds.