The correct timing of the diesel injection pump on engine is of major importance for all functions of the engine and for its exhaust emissions, during production pass off as well as in the field. Within the diesel service workshops a variety of devices exist to test the timing of the injection pump on engine. Most of them operate by clamp-on transducer being fitted to the injection pipe.A large uncertainty exists concerning the accuracy of such timing systems. Most diesel engine manufacturers do not have confidence in the timing devices capability and, therefore, do not recommend their usage.A working group within the International Organization for Standardization (ISO) adopted a method for the validation of these measurement systems, which usually is used to judge the capability of measurement gauges for industrial production processes.The clamp-on systems fail marginally to fulfill the statistical demands of a production process but may be considered satisfactory for use as a service diagnostic instrument, which generally needs not be verified against the ambitious demands of production settings.The dynamic timing systems have shown to be superior to some conventional, static-mechanical timing procedures, given the right conditions. They could well serve as an in-service measurement system, if the nominal errors in the readings between devices of different manufacturers could be avoided.