  In this article we provide various analytical and numerical methods for
calculating the average drift of magnetically trapped particles across field
lines in complex geometries, and we compare these methods against each other.
To evaluate bounce-integrals, we introduce a generalisation of the trapezoidal
rule which is able to circumvent integrable singularities. We contrast this
method with more standard quadrature methods in a parabolic magnetic well and
find that the computational cost is significantly lower for the trapezoidal
method, though at the cost of accuracy. With numerical routines in place, we
next investigate conditions on particles which cross the computational
boundary, and we find that important differences arise for particles affected
by this boundary, which can depend on the specific implementation of the
calculation. Finally, we investigate the bounce-averaged drifts in the
optimized stellarator NCSX. From investigating the drifts, one can readily
deduce important properties, such as what subset of particles can drive
trapped-particle modes, and in what regions radial drifts are most deleterious
to the stability of such modes.
