Chairs of series 309 were especially developed for the use in operating theatres. These chairs come with manifold adjustably armrests which support the relief of the shoulders, neck muscles and spinal discs of the surgeon. The polsters can be adjusted sideways by 9 cm and by approximately 40° backwards as well as by 45° forewards. They can also be adjusted in height by 17 cm and rotate by 360°. The backrest which has a cushioning effect can be adjusted in height by 9 cm and in depth by 3 cm. The seat can be inclined according to the weight of the user with the help of a lever. The chair is electroconductive. The height adjustment is either done by a foot release or by a hand release which is situated under the seat.