An adjustable article includes a frame, a one movable support pivotally mounted for adjustment with respect to the frame, curved guides connected to respective opposite lateral sides of the movable support section, bearings connected to respective opposite lateral sides of the frame, the curved guides arranged to run on the bearings to permit adjustment about a pivot axis defined by the centre of curvature of the curved guides, and captivating means for maintaining engagement of the guides on the bearing means through the range of adjustment. The captivating means comprises, on each lateral side of the frame, a means for resisting sideways lateral movement of the respective curved guide with respect to the frame, a roller bearing is fixed in relation to the frame and arranged to bear on the respective curved guide to maintain the curved guide in the plane of the bearing means associated with that guide.
