  We explain the origin of the controversy about the existence of a transverse
angular momentum sum rule, and show that it stems from utilizing an incorrect
result in the literature, concerning the expression for the expectation values
of the angular momentum operators. We demonstrate a new, short and direct way
of obtaining correct expressions for these expectation values, from which a
perfectly good transverse angular momentum sum rule can be deduced. We also
introduce a new classification of sum rules into primary and secondary types.
In the former all terms occurring in the sum rule can be measured
experimentally; in the latter some terms cannot be measured experimentally.
