  The software tool GRworkbench is an ongoing project in visual, numerical
General Relativity at The Australian National University. This year,
GRworkbench has been significantly extended to facilitate numerical
experimentation. The numerical differential geometric engine has been rewritten
using functional programming techniques, enabling fundamental concepts to be
directly represented as variables in the C++ code of GRworkbench. Sophisticated
general numerical methods have replaced simpler specialised algorithms. Various
tools for numerical experimentation have been implemented, allowing for the
simulation of complex physical situations.
  A recent claim, that the mass of the Milky Way can be measured using a small
interferometer located on the surface of the Earth, has been investigated, and
found to be an artifact of the approximations employed in the analysis. This
difficulty is symptomatic of the limitations of traditional pen-and-paper
analysis in General Relativity, which was the motivation behind the original
development of GRworkbench. The physical situation pertaining to the claim has
been modelled in a numerical experiment in GRworkbench, without the necessity
of making any simplifying assumptions, and an accurate estimate of the effect
has been obtained.
