The C4 facility is made of a vertical axis jet and used to calibrate pneumatic and fast response directional probes up to the transonic domain. It is installed next to the C3 blowdown cascade facility, and benefits from the same 40 bar air supply system. The air coming from this high pressure air reservoir enters into a settling chamber through a perforated cylinder. Several grids are installed in this section to control and guarantee the uniformity of the flow and the turbulence. The calibration nozzle is characterized by a contraction ratio equal to 14.75 and presents an outlet diameter equal to 50 mm, allowing a stable operation, even at high Mach numbers. Large mass flows can be maintained during significant times (up to a few minutes). Three different computerized carriages allow running a detailed angular (yaw and pitch) calibration. The accuracy quoted in the angle calibration is better than +/- 0.5 deg.