a: definition of inclination angle i for our synthetic predictions in Sect. 3. b: sketch illustrating the construction of the transverse PV cut at projected altitude z_cut with a Gaussian beam θ_b. Wind rotation induces different line-of-sight velocities at symmetric offsets + r and − r on either side of the jet axis, producing a detectable “tilt” in the PV cut (see Fig. 4). This projected velocity shift is used to estimate the rotation speed and specific angular momentum of the flow (see Sect. 3.2). Adapted from Ferreira (2001).