  Presented here is a technique of propagating uncertainties through the parton
shower by means of an alternate event weight. This technique provides a
mechanism to systematically quantify the effect of variations of certain
components of the parton shower leading to a novel approach to probing the
physics implemented in a parton shower code and understanding its limitations.
Further, this approach can be applied to a large class of parton shower
algorithms and requires no changes to the underlying implementation.
