S-shaped is not a marketing shape here; the 17 by 21.5 inch backrest bends twice, once to catch the shoulder blades and once to fill the lumbar hollow. Twist the control knob and it rocks between 90 and 105 degrees, enough motion to unstick a stiff back without tipping you out of typing range. Leathaire on the outside stays breathable and takes a damp cloth; high-density sponge underneath gives soft support. Armrests are streamlined and wear zippered covers, standing 26.5 to 30.5 inches high with 22 inches between them. The 19 by 16.5 inch seat lifts from 19 to 22.5 inches and spins 360 degrees, and five universal wheels plus a back handle make relocation easy. Rated to 330 lbs, the chair is 26.5 inches square, 41.5 inches at its tallest, 27.5 lbs. The rocking tension knob lets the sitter change how the S-shaped backrest moves. Seat height: 19"-22.5"; Seat size: 19" x 16.5"