  The possibility of using astrophysical observations of rotational transitions
in the methanol molecule to measure, or constrain temporal and spatial
variations in the proton-to-electron mass ratio (mu) has recently been
investigated by several groups. Here we outline some of the practical
considerations of making such observations, including both the instrumental and
astrophysical limitations which exist at present. This leads us to conclude
that such observations are unlikely to be able to improve evidence either for,
or against the presence of variations in the proton-to-electron mass ratio by
more than an order of magnitude beyond current limits.
