Uncertainty on σ_int,0, σ_env,0, χ_lum, and χ_red (from the top to the bottom) as a function of the observational uncertainty σ_noise and the number of lines of sight N_los for an overall extragalactic Faraday depth variance of ≈7.0 rad m^-2 (left panels) and ≈0.7 rad m^-2 (right panels). The size of the points is proportional to the uncertainty on the parameter. A description of this uncertainty is given also by the grayscale. Circles refer to scenarios including two components, while triangles refer to three-component scenarios. Continuous lines correspond to = const.