Abstract: This invention is concerned with an indicator apparatus for determination of the trajectory or the trajectory direction of a projectile travelling at supersonic speed. It comprises pressure sensitive transducers (T.sub.1 -T.sub.4), which have fixed positions relative to each other or move relative to each other in a defined way, and which are devised to measure the pressure wave generated by the projectile. Also, there are means to produce electrical signals from the transducers, which represent the pressure values sensed by the transducers. Using said signals from each pressure transducer the computing circuits determine a value for a time instance when the pressure wave pass the transducer. From these time values and the geometrical quantities, which specify the position of each transducer in relation to a spatial coordinate system, the computing circuits evaluate the direction of the projectile trajectory more or less accurately.