Abstract: A positioning device is used for the positioning of a chair seat as to its inclination, or for positioning a back-rest member of a chair. The positioning device is constructed such as usual hydropneumatic springs which can be locked by closing a passage connected to working chambers on both sides of a piston. The working chambers are filled with an operating liquid. In order to adapt the biasing force of such a positioning device, one of the working chambers is conneced with a force-measuring device, which force measuring device is provided within the force transmission path of the respective chair column. The force measuring device comprises a measuring space filled with operating liquid, and this operating liquid is in liquid connection with one of the working chambers.