Stokes Q maps illustrating the validation on mock data. Top row, left to right: one realisation of the noisy mock data, the noise-free Vansyngel model, and the result of the FoCUS algorithm. Bottom row, left to right: noise map used in the data simulation, the correction found by the FoCUS method, and the residual map, i.e. the difference between the Vansyngel model and the FoCUS map.