The quality of the data products is primarily determined by the quality of the background subtraction. This is indicated by the QFLAG field which has been filled after visual examination of all the products. QFLAG has a range of 0 to 5 (no background subtraction to excellent; see table 3). Observations with a QFLAG less than 3 are usually not of sufficient quality for spectral and/or timing analysis and the experienced user is recommended to re-subtract the background from the cleaned data cubes for spectral and/or timing analysis.
A reconstructed photon spectrum is shown in figure 7 as an example of a GINGALAC dataset of unusable quality (QFLAG = 1). In this example, the top-layer spectrum is much harder than the mid-layer spectrum at energies above keV, and the mid-layer spectrum has significant counts below keV. Clearly, this dataset has been poorly background subtracted. The source observation prior to this example showed a significant decrease in the SUD rate between the two observations. Therefore, because the SUD rate is an important factor in the determination of the background level (see section 2.4), this dataset is considered unusable and should not be used.