It is disclosed a device for determining an axis joining origins of at least two reference systems (Ref1, Ref2) of a rigid body (T). The device comprises at least a first and a second inertial sensor (1, 2), provided with a triaxial accelerometer and a triaxial gyroscope, predisposed to be constrained to the rigid body (T) and for respectively defining the first and the second reference system. The device further comprises a processing unit (3), connected to the inertial sensors (1, 2). The processing unit comprises an acquiring module (31) configured to acquire first data (d1) representing angular velocities and second data (d2) representing linear accelerations of the rigid body (T) detected by the first and second inertial sensor (1, 2) during a movement of the rigid body (T) itself, comprises a first calculating module (32) configured to calculate third data (d3) representing angular accelerations of the rigid body (T) as a function of the first data (d1) acquired, comprises a second calculating module (36) configured to calculate a relative orientation between the first and the second reference system (Ref1, Ref2) as a function of the first data (d1), comprises a third calculating module (33) configured to calculate a vector (V1) which joins origins (Ο1, O2) of the first (Ref1) and of the second (Ref2) reference system as a function of the first, second and third data (d1, d2, d3) and as a function of the relative orientation calculated between the first and the second reference system (Ref1, Ref2), wherein the primary direction (DIR_1) of the primary vector (V1) is representative of the axis joining the origins of the two reference systems (Ref 1, Ref2).L'invention concerne un dispositif permettant de déterminer un axe reliant les origines d'au moins deux systèmes de référence (Ref1, Ref2) d'un corps rigide (T). Le dispositif comprend au moins un premier et un deuxième capteur inertiel (1, 2) pourvus d'un accéléromètre triaxial et d'un gyroscope triaxial, préd
