the BOSS-DR12 at $z_{\rm eff} = 0.38$, $z_{\rm eff} = 0.51$, and at $z_{\rm eff} = 0.61$ [@Alam:2016hwk]. The distance ratio $D_{\rm V}(z)/r_{\rm s}(z_{\rm d})$ or $D_{{\rm M}}(z)/r_{\rm s}(z_{\rm d})$ for the BAO data are shown in Table \[bao\].

    $z$                             $\xi(z)$                             Experiment      Reference
  ------- ------------------------------------------------------------- ------------ ------------------
   0.106       $D_{\rm{V}}(z)/r_{\rm s}(z_{\rm d})=2.976\pm0.133$          6dFGS         [@Beutler]
   0.15        $D_{\rm{V}}(z)/r_{\rm s}(z_{\rm d})=4.466\pm0.168$         SDSS-DR7     [@Ross:2014qpa]
   0.38    $D_{\rm{M}}(z)/r_{\rm s}(z_{\rm d})=10.231\pm0.149\pm0.074$   BOSS-DR12     [@Alam:2016hwk]
   0.51    $D_{\rm{M}}(z)/r_{\rm s}(z_{\rm d})=13.364\pm0.183\pm0.095$   BOSS-DR12     [@Alam:2016hwk]
   0.61    $D_{\rm{M}}(z)/r_{\rm s}(z_{\rm d})=15.611\pm0.223\pm0.115$   BOSS-DR12     [@Alam:2016hwk]

![image](ELTvsSKA.pdf){width="8cm"}

The $\chi^{2}$ function for BAO measurements is $$\chi^2_{\rm BAO}=\sum\limits_{ i=1}^5 \frac{(\xi^{\rm obs}_{ i}-\xi^{\rm th}_{ i})^2}{\sigma_{ i}^2},$$ where $\xi_{\rm th}$ and $\xi_{\rm obs}$ represent the theoretically predicted value and the experimentally measured value of the $i$-th data point for the BAO observations, respectively, and $\sigma_{i}$ is the standard deviation of the $i$-th data point.

Redshift drift observations from E-ELT and SKA
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The actual measurement for the SL-test signal is the shift in the spectroscopic velocity ($\Delta v$) for a source in a given time interval ($\Delta t_o$). The spectroscopic velocity shift is usually expressed as [@Loeb:1998bu] $$\label{3}
   \Delta v=\frac{\Delta z}{1+z} =H_{\rm{0}} \Delta t_{o} \left[1-\frac{E(z)}{1+z}\right],$$ where $E(z)$ is determined by a specific cosmological model.

The measurement of velocity shift will be achieved by 