  The locations of the peaks of the CMB spectrum are sensitive indicators of
cosmological parameters, yet there is no known analytic formula which
accurately describes their dependence on them. We parametrize the location of
the peaks as l_m = l_A(m - \phi_m), where l_A is the analytically calculable
acoustic scale and m labels the peak number. Fitting formulae for the phase
shifts \phi_m for the first three peaks and the first trough are given. It is
shown that in a wide range of parameter space, the acoustic scale l_A can be
retrieved from actual CMB measurements of the first three peaks within one
percent accuracy. This can be used to speed up likelihood analysis. We describe
how the peak shifts can be used to distinguish between different models of dark
energy.
