  As more than half of the Fluorescence Detector (FD) of the Auger Observatory
is completed, data taking is becoming a routine job. It is then necessary to
follow strict procedures to assure the quality of the data. An overview of the
data taking methods is given. The nature of the FD background signal is due to
the night sky brightness (stars and planet faint light, moonlight, twilight,
airglow, zodiacal and artificial light) and to the electronic background
(photomultiplier and electronic noise). The analysis of the fluctuations in the
FADC signal (variance analysis), directly proportional to the background mean
light level, performed for each night of data taking is used to monitor the FD
background signal. The data quality is analysed using different techniques,
described in detail. Examples of trigger rates, number of stereo events, dead
time due to moonlight, weather or hardware problems are given. The analysis
comprises several months of data taking, giving an overview of the FD
capabilities, performance and allowing a systematic study of data and their
correlation with the environment.
