  We study the number of zeroes of a stationary Gaussian process on a long
interval. We give a simple asymptotic description of the variance of this
random variable, under mild mixing conditions. In particular, we give a linear
lower bound for any non-degenerate process. We show that a small (symmetrised)
atom in the spectral measure at a special frequency does not affect the
asymptotic growth of the variance, while an atom at any other frequency results
in maximal growth. Our results allow us to analyse a large number of
interesting examples. We state some conjectures which generalise our results.
