A lithographic apparatus or frame assembly, comprising: a first and second pneumatic support, being arranged to control position of a frame, each of said pneumatic supports accommodating a pressure chamber; a frame position control system, comprising; a first position sensor device, configured to generate measurement data relating to the position of the frame; a first pressure controller, configured to control the pressure in the pressure chamber of the first pneumatic support on the basis of the measurement data generated by the first position sensor device; a pressure differential sensor device, configured to generate data relating to the difference between the pressure in the pressure chambers of the first and the second pneumatic support; a second pressure controller, configured to control the pressure in the pressure chamber of the second pneumatic support on the basis of the measurement data from the pressure differential sensor device.