Abstract: According to a method and a device for deciding relative to a chosen reference system, and without contact, the position, direction or speed—or any combination thereof—for a projectile (10) in its flight through a gas towards a giver target (30), the position of the projectile in a first plane (35) is decided at a certain distance from the target by means of at least three acoustic sensors (S1, S2, S3) arranged in a vicinity of the plane. Acoustic sound waves, emanating from a turbulent gas volume (13, 14, 15) extending essentially straight behind the projectile (10), and/or emanating from a wake or monopole (12, 13) existing essentially straight behind the projectile, are received by means of the acoustic sensors (S1, S2, S3). Time differences for the arrival of the acoustic sound waves to the respective acoustic sensors are measured. The projectile position (x, y; x1, y1) in the first plane is calculated from the time differences.