  We simulate crystallisation of hard spheres with short-ranged attractive
potentials, as a model self-assembling system. We show how measurements of
correlation and response functions during assembly can be used to tune the
interaction parameters as assembly proceeds, in order to obtain high-quality
crystals. The method we use is independent of details of the interaction
potential and of the structure of the final crystal - we propose that it could
be applied to a wide range of self-assembling systems.
