Top panel: histogram of the EW of Hγ(4340 Å) for 122,846 OB star candidates (black) and 21,690 identified normal OB stars (red) and 101,156 non-OB (blue) stars. Bottom panel: histogram of the EW of He I (4471 Å) for 122,849 OB star candidates (black), 21,690 identified normal OB stars (red), and 101,159 non-OB (blue) stars.