  We give an explicit formula for the exponents (i.e. the spectra up to the
shift by one) of an irreducible plane curve singularity in terms of Puiseux
pairs. As an application we prove in this case Hertling's conjecture that the
variance (i.e. the square of the standard deviation) of the exponents is
bounded by the difference between the maximal and minimal exponents divided by
12.
