  As the data on CMB anisotropies improve and potential cosmological
applications are realized, it will be increasingly important for theoretical
calculations to be as accurate as possible. All modern calculations for
inflationary-inspired fluctuations involve the numerical solution of coupled
Boltzmann equations. There are many assumptions and choices to be made when
carrying out such calculations. We go through each in turn, pointing out the
best selections to make, and the level of inaccuracy expected through incorrect
choice: (1) neglecting the effects of neutrinos or polarization has a 10%
effect; (2) varying radiation temperature and He fraction can have smaller, but
noticeable effects; (3) numerical issues, such as k-range and smoothing are
discussed; (4) short-cut methods, e.g. free-streaming and tilt approximations,
are generally inadequate at the few % level; (5) at the 1% level somewhat
baroque effects are important, such as He recombination and even minimal
reionization; (6) at smaller angular scales there are secondary effects which
will ultimately have to be considered. Extracting information from the
subsidiary acoustic peaks and the damping region will be an extremely
challenging problem. However, given the prospect of measuring just such
information on the sky, it will be important to meet this challenge. In
principle we can obtain details about reionization history, neutrino
contribution, helium abundance, non-power-law initial conditions etc.
