  We present a systematic study of differences between NLL resummation and
parton showers. We first construct a Markovian Monte-Carlo algorithm for
resummation of additive observables in electron-positron annihilation.
Approximations intrinsic to the pure NLL result are then removed, in order to
obtain a traditional, momentum and probability conserving parton shower based
on the coherent branching formalism. The impact of each approximation is
studied, and an overall comparison is made between the parton shower and pure
NLL resummation. Differences compared to modern parton-shower algorithms
formulated in terms of color dipoles are analyzed.
