atmospheres and photospheres (e.g. @Konstantinova2010 [@Lebre2014; @Sabin2015a]), analysis of the linearly polarized emission of circumstellar dust and molecules (e.g. @Vlemmings2012 [@Vlemmings2017; @Girart2012; @Sabin2014]). Nevertheless, we are still far from getting a full picture of the effects of magnetic fields in evolved stars. Small samples (compared to the total number of stars at each evolutionary stage) and few global analyses (combining the different techniques aforementioned), are likely the main causes for this. For instance, only two pAGBs are known to show a clear Zeeman splitting profile, and hence allow a definite magnetic field detection at their surface [@Sabin2015a]. This number plummets to zero when it comes to the central stars of PNe [@Leone2011; @Jordan2012; @Leone2014; @Steffen2014].\
In this context the post-AGB OH 231.8+4.2 (a.k.a the Calabash nebula) establishes itself as a key object of study based on the various polarimetric observations that have been performed along the years. Indeed, this is one of the few objects for which numerous maser and dust polarization analysis have been undertaken, allowing for a unique view of its magnetic field.\
OH 231.8+4.2 is a bipolar oxygen-rich binary pAGB and has been the subject of maser and dust continuum polarization analyses targeting both the strength and 