Display of PCN vs. E_M for the solar cycle epoch 1997–2009. Dashed line indicates equality. Square dots mark bin averages, error bars indicate standard deviation within every other bin. The curve of large red dots shows common reference (Eq. (6) with E_C = 10.5 mV/m), while the curve of smaller dots indicates best fit between the function in Eq. (6) (with variable E_C) and the bin average PCN values. The parameters from the fit, E_C and the minimum weighted RMS deviation are noted in the plots.