Theoretical curves of growth of the Mg lines at 5528 and 5711 Å. The curves correspond to the star BD+09 2870, the parameters of which are given in the plot. The thick and thin lines represent NLTE and LTE, respectively. The NLTE curve of the line at 5711 Å is marked by the dashed line. The crosses symbols indicate REW and corresponding Mg abundances in LTE and NLTE for each line; values are noted in the plot.