Median values of the difference between observed and true metallicity as a function of the true values of metallicity at z = 0.70 and S/N_I,obs = 10. The black error bars indicates the main case of our work, while the red dashed error bars represent the case excluding indices below 3000 Å. The blue vertical dashed line marks the solar metallicity value ([Z/H] = 0). The green dashed line represents the 0 value of the y-axis.