Sketch of a slice of the ellipsoidal shell model across the plane including its major axis and tilt direction. The geometry of the ellipsoid is defined by the semi-major axis a, semi-minor axis b, their ratio e, and the inclination angle i with the line of sight, illustrated on the sketch. The singular measurables projected semi-major axis r^max, maximum systemic radial velocity $V_{\text{r}}^{\max }$, and radial distance at maximum systemic radial velocity $r^{V_{\text{r}}^{\max }}$ are also labeled.