  Tsallis has proposed a generalisation of the standard entropy, which has
since been applied to a variety of physical systems. In the canonical ensemble
approach that is mostly used, average energy is given by an unnromalised, or
normalised, $q$-expectation value. A Lagrange multiplier $\beta$ enforces the
energy constraint whose physical interpretation, however, is lacking. Here, we
use a microcanonical ensemble approach and find that consistency requires that
only normalised $q$-expectation values are to be used. We then present a
physical interpretation of $\beta$, relating it to a physical temperature. We
derive this interpretation by a different method also.
