... The investigation of the utility of SPYBALs in keeping the spectrum centered on the diode array focused on two areas: 1) the change in SPYBAL offset with time and 2) the degree to which an individual spectrum may be tilted with respect to the diode array. ... ZSPYBLU records the offset amount, in y-deflection units, which the spectrum was moved from its nominal position in order to center it on the array. ... ZSPYBLU values for Side 2 GHRS grating G270M over time. ... SPYBAL Drift with Time . ...