  We study the statistical fluctuations (such as the variance) of causal set
quantities, with particular focus on the causal set action. To facilitate
calculating such fluctuations, we develop tools to account for correlations
between causal intervals with different cardinalities. We present a convenient
decomposition of the fluctuations of the causal set action into contributions
that depend on different kinds of correlations. This decomposition can be used
in causal sets approximated by any spacetime manifold $\mathcal M$. Our work
paves the way for investigating a number of interesting discreteness effects,
such as certain aspects of the Everpresent $\Lambda$ cosmological model.
