Characterization of precision premium in astrometry
  Precision premium, a concept in astrometry that was firstly presented by
Pascu in 1994, initially means that the relative positional measurement of the
Galilean satellites of Jupiter would be more accurate when their separations
are small. Correspondingly, many observations have been obtained of these
Galilean satellites since then. However, the exact range of the separation in
which precision premium takes effect is not clear yet, not to say the variation
of the precision with the separation. In this paper, the observations of open
cluster M35 are used to study precision premium and the newest star catalogue
Gaia DR2 is used in the data reduction. Our results show that precision premium
does work in about less than 100 arcsecs for two concerned objects, and the
relative positional precision can be well fitted by a sigmoidal function.
Observations of Uranian satellites are also reduced as an example of precision
premium.
