Regulation No 24 of the Economic Commission for Europe of the United Nations (UN/ECE) — Uniform provisions concerning: I. The approval of compression ignition (C.I.) engines with regard to the emission of visible pollutants — II. The approval of motor vehicles with regard to the installation of C.I. engines of an approved type — III. The approval of motor vehicles equipped with C.I. engines with regard to the emission of visible pollutants by the engine — IV. The measurement of power of C.I. engines