  A method of indirect measurement of the light quark running mass $\hat{m} =
(m_d + m_u)/2$ is elaborated in detail. It is based on measuring 1\%-level
azimuthal angular asymmetries in the decay $\tau \rightarrow \nu_\tau + 3\pi$.
The latter are then used in QCD sum rules to obtain experimental lower bounds
for $\hat{m}$. For a sample of $2.5 \times 10^5$ $\tau \rightarrow \nu_\tau +
3\pi$ decays free of background, the resulting statistical error in the bound
for $\hat{m}$ is estimated to be 1 MeV, i.e., comparable to the systematic
error due to the use of QCD sum rules. Contribution to the Third Workshop on
the $\tau$ Charm Factory 1-6 June 1993, Marbella, Spain.
