  The Gaia-Tycho release, scheduled for 14 September, is forecast to yield
parallax errors of $\sigma(\pi)\sim 300\,\mu$as for about 2 million Tycho
stars. We show analytically that the actual performance should be $$
\sigma(\pi) = {\rm max}(\sigma_{1991}/96,20\,\mu{\rm as}) $$ where
$\sigma_{1991}$ is the positional error from the Hipparcos mission. For typical
Tycho stars, $\sigma_{1991}\sim 30\,$mas, so this reproduces the usual claims.
However, for the 100,000 star Hipparcos subset of this sample, $\sigma_{1991}$
is a factor 15 or more smaller. These much lower Hipparcos positional errors
apply even to stars at the Hipparcos-Tycho limit, $V\sim 12$. This is
especially important for RR Lyrae stars, as well as other special classes, that
were systematically included in the Hipparcos catalog down to this limit
because of their exceptional scientific importance. This predicted performance
will provide an early test of the Gaia algorithms.
