  We examine systematic problems in determining the local matter density from
the vertical motion of stars, i.e. the 'Oort limit'. Using collisionless
simulations and a Monte Carlo Markov Chain technique, we determine the data
quality required to detect local dark matter at its expected density. We find
that systematic errors are more important than observational errors and apply
our technique to Hipparcos data to reassign realistic error bars to the local
dark matter density.
