@Carnero; @Sanchez11], we obtained a robust and moderately significant measurement of the BAO angular scale, $\theta_{\mbox{\footnotesize\sc bao}} = 1.77^{\circ} \pm 0.31^{\circ}$ at $\overline{z}=2.225$, using the excellent catalogue DR12Q of the SDSS collaboration. The statistical significance of this measurement, $2.12 \,\sigma$, i.e., 97% confidence level, was calculated with the non-linear theoretical covariance matrix expected in the $\Lambda$CDM concordance model (see section \[errors\]), a result that is in excellent agreement with reported measurements (see, e.g., refs. [@Carnero; @Crocce11b]).

After measuring the acoustic peak position through the 2PACF, it was necessary to apply a shift correction due to unavoidable projection effects caused by the finite thickness of the redshift shell, $\delta z \ne 0$, of the quasars sample. But, as expected from previous analyses [@Sanchez11], the numerical evaluation of this effect showed a negligible shift correction of less than 1%, evidencing a weak dependence of our measurement with respect to the reference cosmological model. At the same time, one observes that the effective model contribution in this approach comes from the sound horizon value, $r_s$, which is derived from CMB measurements in a model-dependent way [@wmap9].

Additionally, we validated our angular BAO detection through diverse robustness tests. In fact, we show in sections 