  We report on our ongoing efforts to ensure that the MICADO NIR imager reaches
differential absolute (often abbreviated: relative) astrometric performance
limited by the SNR of typical observations. The exceptional 39m diameter
collecting area in combination with a powerful multi-conjugate adaptive optics
system (called MAORY) brings the nominal centroiding error, which scales as
FWHM/SNR, down to a few 10 uas. Here we show that an exceptional effort is
needed to provide a system which delivers adequate and calibrateable
astrometric performance over the full field of view (up to 53 arcsec diameter).
