  For the theoretical prediction of cross-section fluctuations in chaotic
scattering, the cross-section autocorrelation function is needed. That function
is not known analytically. Using experimental data and numerical simulations,
we show that an analytical approximation to the cross-section autocorrelation
function can be obtained with the help of expressions first derived by Davis
and Boose. Given the values of the average S-matrix elements and the mean level
density of the scattering system, one can then reliably predict cross-section
fluctuations.
