  The two-terminal conductance of a random flux model defined on a square
lattice is investigated numerically at the band center using a transfer matrix
method. Due to the chiral symmetry, there exists a critical point where the
ensemble averaged mean conductance is scale independent. We also study the
conductance distribution function which depends on the boundary conditions and
on the number of lattice sites being even or odd. We derive a critical exponent
$\nu=0.42\pm 0.05$ for square samples of even width using one-parameter scaling
of the conductance. This result could not be obtained previously from the
divergence of the localization length in quasi-one-dimensional systems due to
pronounced finite-size effects.
