By F0, the hydrogen lines have lost most of their sensitivity to luminosity. Note, however, that they can still be used to distinguish the supergiant classes from lower luminosities. Near F0, the luminosity class is estimated from the strength of lines due to ionized iron and titanium. Excellent luminosity-sensitive features include the Fe II, Ti II double blend at 4172-8, and similar blends at 4395-4400, 4417 and 4444. The strength of these blends are usually estimated with respect to other less luminosity sensitive features, such as Ca I 4227, Fe I 4271 and Mg II 4481.