  Counts-in-cells (CIC) measurements contain a wealth of cosmological
information yet are seldom used to constrain theories. Although we can predict
the shape of the distribution for a given cosmology, to fit a model to the
observed CIC probabilities requires the covariance matrix -- both the variance
of counts in one probability bin and the covariance between counts in different
bins. To date, there have been no general expressions for these variances. Here
we show that correlations of particular levels, or "slices," of the density
field determine the variance and covariance of CIC probabilities. We derive
explicit formulae that accurately predict the variance and covariance among
subvolumes of a simulated galaxy catalog, opening the door to the use of CIC
measurements for cosmological parameter estimation.
