Synchronization mechanism for a correlated seat-backrest movement of an office chair, comprising a base support that can be placed on a chair column , a seat support and a backrest support , wherein the backrest support is pivotably connected to the base support , defining the main axis of rotation of the synchronization mechanism as a result, comprising a coupling device having a first coupling element , operatively connected to the backrest support , and a second coupling element , operatively connected to the base support , wherein the first coupling element and the second coupling element are connected to each other in an articulated manner at a connecting point , wherein the first coupling element is articulated to the backrest support at a distance from the connecting point and, in a pivoting movement of the backrest support occurring from a non-pivoted basic position into a position pivoted rearward, as viewed in the seat longitudinal direction , pulls the connecting point of the two coupling elements forward, as viewed in the seat longitudinal direction , and wherein the second coupling element is supported by an adjustment end at a distance from the connecting point on a support point of the base support , and comprising a spring assembly for defining the pivoting resistance of the backrest support , wherein the spring assembly has at least one spring element , wherein the spring element has a stationary end and a free end , wherein the free end acts on the connecting point of the coupling device , characterized by an adjustment mechanism for setting the spring force of the at least one spring element , wherein the adjustment mechanism has a web element attached movably to the base support , on which element the support point is located. comprising a coupling device having a first coupling element , operatively connected to the backrest support , and a second coupling element , operatively connected to the base support , wherein the first coupling element and the second coupling element are connected to each other in an articulated manner at a connecting point , wherein the first coupling element is articulated to the backrest support at a distance from the connecting point and, in a pivoting movement of the backrest support occurring from a non-pivoted basic position into a position pivoted rearward, as viewed in the seat longitudinal direction , pulls the connecting point of the two coupling elements forward, as viewed in the seat longitudinal direction , and wherein the second coupling element is supported by an adjustment end at a distance from the connecting point on a support point of the base support , and comprising a spring assembly for defining the pivoting resistance of the backrest support , wherein the spring assembly has at least one spring element , wherein the spring element has a stationary end and a free end , wherein the free end acts on the connecting point of the coupling device , characterized by an adjustment mechanism for setting the spring force of the at least one spring element , wherein the adjustment mechanism has a web element attached movably to the base support , on which element the support point is located. <EOS>