  When averages of different experimental determinations of the same quantity
are computed, each with statistical and systematic error components, then
frequently the statistical and systematic components of the combined error are
quoted explicitly. These are important pieces of information since statistical
errors scale differently and often more favorably with the sample size than
most systematical or theoretical errors. In this communication we describe a
transparent procedure by which the statistical and systematic error components
of the combination uncertainty can be obtained. We develop a general method and
derive a general formula for the case of Gaussian errors with or without
correlations. The method can easily be applied to other error distributions, as
well. For the case of two measurements, we also define disparity and
misalignment angles, and discuss their relation to the combination weight
factors.
