  Prompted by a recent paper by Dima and Schad, we re-consider the problem of
inferring magnetic properties of the corona using polarimetric observations of
magnetic dipole (M1) lines. Dima and Schad point to a potential source of
degeneracy in a formalism developed by Plowman, which under some circumstances
can lead to the solution being under-determined. Here we clarify the nature of
the problem. Its resolution lies in solving for the scattering geometry using
the elongation of the observed region of the corona. We discuss some conceptual
problems that arise when casting the problem for inversion in the observer's
reference frame, and satisfactorily resolve difficulties identified by Plowman,
Dima and Schad.
