  We propose a method to determine the quantum numbers, which we call the
rigged configurations, for the solutions to the Bethe ansatz equations for the
spin-1/2 isotropic Heisenberg model under the periodic boundary condition. Our
method is based on the observation that the sums of Bethe's quantum numbers
within each string behave particularly nicely. We confirm our procedure for all
solutions for length 12 chain (totally 923 solutions).
