After you've set the chair height, move on to lumbar support. The lumbar area of the back should be supported to hold its normal curve and prevent a rounded shape. This reduces muscle fatigue and encourages a straighter posture while seated.
The lumbar height and lumbar depth are the next variables, which mechanically allow the lumbar support shape to be adapted to the user's back shape. At the correct seat height, this generally results in a more comfortable sitting position.