Applying the mean surface density of companions, sigma(r), to the
dynamical evolution of star clusters is an interesting approach to
quantifying structural changes in a cluster. It has the advantage
that the entire density structure, ranging from the closest binary
separations, over the core-halo structure through to the density
distribution in moving groups that originate from clusters, can be
analysed coherently as one function of the stellar separations r.
This contribution assesses the evolution of sigma(r) for clusters
with different initial densities and binary populations. The changes
in the binary, cluster and halo branches as the clusters evolve are
documented using direct N-body calculations, and are correlated with
the cluster core and half-mass radius. The location of breaks in the
slope of sigma(r) and the possible occurrence of a binary gap can
be used to infer dynamical cluster properties.