As with any quantum mechanical observable, in order to discuss position measurement, we need to calculate the spectral resolution of the position operator X : D X → → L 2 ( R , C ) : ψ ψ ↦ ↦ x ψ ψ which is X = ∫ ∫ R λ λ d μ μ X ( λ λ ) = ∫ ∫ R x μ μ X = μ μ X ( x ) , where μ μ X is the so-called spectral measure of the position operator.