Summary: The scientific requirements for the basic angle stability and the monitoring of basic angle variations are reviewed in light of the need for absolute parallax determination, which is a primary goal of Gaia. Requirements are proposed for the random and systematic basic angle variations, and for the measurement of these variations.

Bibtex entry for this abstract:

@UNPUBLISHED{LL:GAIA-LL-057,
editor = {L.~Lindegren},
title={{S}cientific requirements for basic angle stability and monitoring},
institution={},
year={2004},
month={December},
url={http://www.rssd.esa.int/doc_fetch.php?id=413563},
note={GAIA-LL-057},
type={Technical note}
}