When measuring magnetic contamination, the index can take an asymmetric positive distribution, with some negative values observed because of air presence. In this example, data from Mar del Plata, Argentina (see [18]), are fitted with a gpower-normal density. Data can be seen in Appendix D. Applying again the methodology detailed in Section 2.4, we obtained an optimum value of 0.19 for the parameter p. The corresponding μ^, σ^ and the 0.25, 0.50 and 0.75 quantiles were 8.05, 1.64 , 3.98, 8.05 and 14.91 respectively.