This part of ISO 29042 specifies a method based on a tracer technique for measuring the capture efficiency of an exhaust system installed on a machine. It is applicable to all types of test environment — test bench, room or field (see ISO 29042-1) — but is only applicable if the tracer shows aerodynamic behaviour comparable to that of the real pollutant. The measurement of the capture efficiency of an exhaust system can serve for a) evaluation of the performance of a machine's exhaust system, b) evaluation of the improvement of an exhaust system, c) comparison of exhaust systems for machines of similar design, d) ranking of exhaust systems according to their capture efficiency, e) determination of the air flow rate of an exhaust system to achieve a given level of capture efficiency, and f) determination of the state-of-the-art of machine exhaust systems with respect to capture efficiency