Identifying spectral discontinuity. Spectra are excluded if ﹩{\rm{\max }}(\left|{\rm{\Delta }}f/p\right|)\gt 1.4﹩ (the red dotted lines), where Δf is the difference of flux f between adjacent points and p is the pixel size (p ∼ 0.16 Å for LAMOST MRS). The left panel shows the max(﹩\left|{\rm{\Delta }}f/p\right|﹩) over 4950–5350 and 6350–6750 Å versus the SNR. The right panels present example spectra with series of max(﹩\left|{\rm{\Delta }}f/p\right|﹩) values.