  We present details for a method to compute the broken phase sphaleron rate
(rate of hot baryon number violation below the electroweak phase transition)
nonperturbatively, using a combination of multicanonical and real time lattice
techniques. The calculation includes the ``dynamical prefactor,'' which
accounts for prompt recrossings of the sphaleron barrier. The prefactor depends
on the hard thermal loops, getting smaller with increasing Debye mass; but for
realistic Debye masses the effect is not large. The baryon number erasure rate
in the broken phase is slower than a perturbative estimate by about exp(-3.6).
Assuming the electroweak phase transition has enough latent heat to reheat the
universe to the equilibrium temperature, baryon number is preserved after the
phase transition if the ratio of (``dimensionally reduced'' thermal) scalar to
gauge couplings (lambda / g^2) is less than .037.
