  The traditional measurement theory interprets the variance as the dispersion
of a measured value, which is actually contrary to a general mathematical
concept that the variance of a constant is 0. This paper will fully demonstrate
that the variance in measurement theory is actually the evaluation of
probability interval of an error instead of the dispersion of a measured value,
point out the key point of mistake in the traditional interpretation, and fully
interpret a series of changes in conceptual logic and processing method brought
about by this new concept.
