real observation, the method identifies and present results from H- and He-like ions falling in the X-rays regime, and differences among 6 % at $\lambda \approx 20$ Åin lines like Ly$_\alpha$ and Ly$_\beta$ of OVIII, to 24 % at $\lambda \approx 10$ Åin lines like MgXI and L-shell of FeXVI-FeXIX, are attributable to the chosen continuum level.

The situation becomes more dramatic as the complexity in absorption increases for model A and model B. We quantify how important this continuum level problem results, where ISM is taking into account. Up to 80 % differences, in both absorbers wabs1 and wabs2, of EW measurements are observed, and it serves as benchmark for comparison of EWs measured using the free-line region (FLR) technique, which make use of absorbed SED as continuum level, as for instance in [@kaspi2002a], for measuring line properties of NGC 3783 (see their Table 1).

Results: Deducing distance from the supermassive black hole {#resul1 .unnumbered}
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In this section we apply our method to the X-ray 900 ks spectrum, introduced in the first section.

Measured [*vs*]{} Theoretical EWs {#measured-vs-theoretical-ews .unnumbered}
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Theoretical curves of the Ratio=$\frac{{\rm EW}_{\rm meas}}{{\rm EW}_{\rm theo}}$ (measured EW to theoretical EW) [*vs*]{} $n_H$, for each 