Next] [GHRS ISR Index] . ... Many times users want to know how long they can observe without a spectrum Y-balance (SPYBAL) in an effort to limit the motion of the carrousel during an observation. This report discusses the rationale for SPYBALS in terms of the drift of the spectrum across the photocathode with time, taking into account the tilt of the spectrum across the diode array. ... Spectrum Tilt Across the Diode Array . Consequences of Tilted Spectra Drifting across the Diode Array . ...