Abstract
The goals of micro-arcsecond space mission rely on the limiting performance associated to the selected instrumental configuration and observing conditions. In particular, variation of the instrumental response over the field, with wavelength and in time, are potentially critical. We discuss the impact on the data quality and how the science data can be used to trace directly and in real time the astrometric instrument response of Gaia. This is one of the driver philosophies behind the Astrometric Instrument Model (AIM) concept. We show results from the test campaigns carried on throughout the 2013.
