The effective oblateness ϵ calculated for different axisymmetric (m = 0) poloidal harmonics calculated with different magnetic field configuration models. Here, I₄₅ = I_*/10⁴⁵ g cm². Filled markers correspond to negative values of ϵ, hollow ones to positive values of ϵ. If one wants to obtain the oblateness produced by non-axisymmetric harmonics, the corresponding value should be multiplied by (l² + l − 3m²)/(l² + l).