Balmer-line profiles for HD 191612 at quiescence (⁠⁠, in black) and near emission maximum (φ= 0.89, red); the tickmarks on the y-axis are separated by half the continuum level. The Hα spectrum of HD 209975 is included to demonstrate that a near match to the minimum-state spectrum can be found among normal stars (see Section 3.2 for details). Difference spectra for Hα and Hζ are shown at the bottom of the plot. Velocities are heliocentric.