Abstract: An adjustment device for a chair, comprising an oscillating mechanism composed of a first plate, associated with a central gas-operated post for the height adjustment of a seat. A second plate is articulated to the first plate so that it can oscillate, by means of a pair of first pivots and is fixed to a backrest. A linkage is articulated to the first plate, by means of a second pivot, and is in turn articulated, by a third pivot, to a third plate, with which the seat can be associated. The third plate is articulated to the second plate. Elements are associated with the linkage for connection to at least one slat or leaf spring, which is arranged on a plane that is substantially parallel to the plane of the seat and is adapted to elastically contrast the inclination of the second plate with respect to the first plate.

Abstract: An adjustment device for a chair, comprising an oscillating mechanism composed of a first plate, associated with a central gas-operated post for height adjustment of a seat, to which a second plate, fixed to a backrest, is articulated so that it can oscillate by a first pivot. A third plate is articulated and interposed, respectively by a second pivot and a third pivot, between the first plate and the second plate, and can be associated with the seat. The first plate has elements for connection to at least one slat or leaf spring which is adapted to elastically contrast the inclination of the second plate with respect to the first plate.