Sign fields of the different reconstructions. Their primary purpose is to capture the sign variations of the Faraday sky. Panel a: field χ of reconstruction I, as defined by the model in Eq. (20). Panel b: field χ of reconstruction II, as defined by the model in Eq. (8). Panel c: field s of the previous reconstruction by NO15, which served a similar purpose. The difference in the scales of these fields is compensated by corresponding differences in the respective Faraday amplitude fields.