Uncertainties in B_LOS due to uncertainties in the input volume density of the chemical evolution code. Top panel: B_LOS variationfor a selection of positions in Orion A sampling regions with different A_V. The x-axis () indicates therelative (%) changes in input density to the chemical model. The y-axis labels the data points presented and corresponds to the positions labeled in Fig. 6. The z-axis plots the change in the magnetic field strength and direction from that calculated for the fiducial density n₀ (10⁴ cm⁻³). The bottom left panel shows B_LOS uncertainties for points with A_V < 1. The bottom right panel shows uncertainties in B_LOS for a selection ofpoints with A_V > 1.