  A complicated and ambitious space mission like Gaia needs a careful
monitoring and evaluation of the functioning of all components of the
satellite. This has to be performed on different time scales, by different
methods, and on different levels of precision. On the basis of housekeeping
data a Quick Look will be performed by the ground segment. A first analyses of
the science data quality and consistency will be done by a Science Quick Look.
However, due to the nominal scanning law a full self-consistent calibration of
the satellite, and a determination of astrometric and global parameters, is not
possible before about half a year has elapsed, imposing a serious danger to
lose valuable observing time if something goes wrong. Therefore, it is
absolutely necessary to perform a Detailed First Look on a daily basis on the
$\mu$as accuracy level. We describe two different methods, a block iterative
procedure and a direct solution, to monitor all satellite parameters that in
principle can be evaluated within a short amount of time, particularly those
that can be measured in along-scan direction. This first astrometric analysis
would greatly benefit from a modified scanning law (Zero-nu-dot mode) for some
time during the commissioning phase.
