  The minimum-bias distribution on heavy ion collision multiplicity $n_{ch}$ is
well approximated by power-law form $n_{ch}^{-3/4}$, suggesting that a change
of variable to $n_{ch}^{1/4}$ may provide more precise access to the structure
of the distribution and to A-A collision centrality. We present a detailed
centrality study of Hijing-1.37 Monte Carlo data at 200 GeV using the power-law
format. We find that the minimum-bias distribution on $n_{participant}^{1/4}$,
determined with a Glauber Monte Carlo simulation, is uniform except for a 5%
sinusoidal variation. The power-law format reveals precise linear relations
between Glauber parameters $n_{part}$ and $n_{bin}$ and the fractional cross
section. The power-law format applied to RHIC data facilitates incorporation of
extrapolation constraints on data and Glauber distributions to obtain a
ten-fold improvement in centrality accuracy for peripheral collisions.
