  Ray Singer torsion is a numerical invariant associated with a compact
Riemannian manifold equipped with a flat bundle and a Hermitian structure on
this bundle. In this note we show how one can remove the dependence on the
Riemannian metric and on the Hermitian structure with the help of a base point
and of an Euler structure, in order to obtain a topological invariant. A
numerical invariant for an Euler structure and additional data is also
constructed.
