In designing for forms in the round it is necessary to detail the ornament on a segment or a stretching-out of the area. This is easily done in the case of a cylinder of which the height is evident, and the extreme width and circumference easily obtainable. If the object is not in existence for direct measurement the width can be determined from the diameter as expressed in the drawing. As this diameter is about one-third of the circumference a parallelogram three times the width of the diameter will provide, in the flat, the complete area on which detail has to be drawn. Should the shape of the object be that of a truncated cone--that is, with straight inclined sides and a circular plan, the procedure must necessarily be different. In this case the lines of the sides should be extended till they intersect. This intersection forms a centre from which arcs may be struck coinciding with the lines of top and base. The greatest diameter should be set off on each side of the elevation on the larger radius and the points joined up with the centres from which the arcs were struck. The result is a fan-shaped figure bounded by these outer lines and the two arcs. This figure gives the entire area of the surface of the truncated cone. In either of the figures thus obtained for designing detail on, the surfaces can be sub-divided. For instance, if the decoration consists of a unit repeated three or six times round the form, it will not be necessary to reproduce the whole area, provided always that the profiles are straight or tapered. [Illustration: No. 226. Method of obtaining a Segment of one-sixth of Vase.] As the diameter is about one-third of the circumference the elevational drawing of the cylinder gives one-third of the area and half a diameter gives one-sixth. In the truncated cone shape the widths are similarly determined, but it will be found that the height, when measured on the centre line, is less than the lengths of the profile lines which constitute the actual height. When the profiles are curved, the procedure is more complicated. As in the case of the cone shape, there is naturally some discrepancy between the height of the elevation and the profile, the actual dimension of which is affected by perspective (as also in plan curvature). To obtain the actual height of the area the profile must be measured vertically with some flexible material, such as thin lead wire, which will readily embrace the curvature. If a division of a third or a sixth is required the diameter or half diameter can be taken, but the segment of the area should be set off on a fresh centre line quite independent of the elevational drawing.