The synchronized mechanism
This mechanism allows a coordinated movement of the back and the seat, with ratio from 1 to 2.5, following the user's movements.
It provides a perfect support of spinal column and the pelvis.
This mechanism can be locked in any position, and it must be possible to adjust the tension according the user's weight.
Generally it includes an anti-return safety device wich avoids a violent return of the backerest when the mechanism is released.