This report presents a relative completeness result for the operator
of projection onto state in Duration Calculus (DC). This operator was
introduced in 1999 and studied extensively in a revised form in 2002
in our earlier works. The completeness of a system of axioms and a
proof rule for projection onto state is established relative to the
extension of DC by neighbourhood formulas, which express the
neighbourhood values of boolean DC state expressions. (Neighbourhood
formulas in DC themselves have a complete axiomatisation relative to
DC.)  The proof of relative completeness is constructive, relative to
validity in DC without extending constructs.