Top panels: temperature sensitivity of the Hδ feature. Over an effective temperature range of 5250 < T_eff (K) < 8000, we expect anincrease in absorption of 31% for a star of logg = 2.50, [Fe/H] = −2.50, and [C/Fe] = 0.0. Middle panels: variation in Ca II H & K line strengths with increasing metallicity for a star of T_eff = 5000 K, log g = 1.0, and [C/Fe] = 0.0. Bottom panels: Ca II H & K line response to increasing effective temperature. The Ca II H line is nearly superposed with Hε.