  A cosmic ray observatory with full-sky coverage can exploit standard
anisotropy analysis methods that do not work if part of the celestial sphere is
never seen. In particular, the distribution of arrival directions can be fully
characterized by a list of spherical harmonic coefficients. The dipole vector
and quadrupole tensor are of special interest, but the full set of harmonic
coefficients constitutes the anisotropy fingerprint that may be needed to
reveal the identity of the cosmic ray sources. The angular power spectrum is a
coordinate-independent synopsis of that fingerprint. The true cosmic ray
anisotropy can be measured despite non-uniformity in celestial exposure,
provided the observatory is not blind to any region of the sky. This paper
examines quantitatively how the accuracy of anisotropy measurement depends on
the number of arrival directions in a data set.
