BXA contour plots for fit parameters of the total model to the Mrk 509 RGS 1 and RGS 2 spectra. The cross-normalization factor shows the difference between two RGS specra where normalization gives the position of the total model. Best fit log $\xi =1.{9829}_{-0.0089}^{+0.0093}$ and log N_H = 20.456 ± 0.016 with z = 0.03374 ± 0.00005 corresponds to the WA outflowing with v = 195 ± 16 km s⁻¹. The diagonal panels show marginalized posterior probability distributions, while off-diagonal panels indicate conditional probability distribution functions among each parameter.