**4. Completely Positive Instrument**

In this section, we analyze the concept of CP instrument in the C∗-algebraic setting. In previous investigations [17–20], it has been examined in the von Neumann algebraic formulation of quantum theory. The generalization to C∗-algebra is realized in terms of central subspaces of the dual of a C∗-algebra. Our approach enables us to unify the measurement theory with sector theory.
