Linking system between two articulations.

The seat has a locking unit and another locking unit (5) respectively positioned on two sides of the seat and locking a backrest relative to a base. The units are synchronized by a shaft (11) and by a transmission rod (6) whose end is fixed to the former unit. A slot including a flat end (13) is placed at another end of the rod. The shaft includes a truncated portion (12) with a flat end (14). The shaft is integrated to the latter unit and extended in a direction of the former unit. The shaft is inserted in the slot with functional clearance absorbing positioning dispersions of the units.