topology of the magnetic field at different scales. @Etoka2009 mapped the distribution of OH masers at 1667 MHz with MERLIN, at an angular resolution of $\sim$0.2 and found a ring-like pattern with a $\sim 4$ diameter centred on the central star. This corresponds to a radius of $\sim$3300 AU considering that OH 231.8+4.2 is part of the open cluster M46 (or NGC 2347, @Jura1985) for which the recent Gaia DR2 release indicates a mean parallax of 0.61 mas [@Cantat2018], leading to a distance to the nebula of 1639 pc. The polarization analysis (circular and linear) indicated a radial magnetic field aligned with the outflow of the pAGB.\
Later on, @Leal2012 observed the H$_{2}$O 6$_{1,6}$–5$_{2,3}$ rotational transition with the Very Long baseline Array (VLBA) and a synthesized beam size of $\sim$1.7$\times$0.9 mas. Of all the 30 detected maser spots, most of them are distributed in the direction of the collimated outflow and at $\sim$40 AU from the central star (assuming a distance of 1540 pc derived by @Choi2012), only a few show detectable level of polarization. Although it was not possible to estimate the direction of the magnetic field via linear polarization analysis, the presence of circular polarization in two masers 