In the field of Prognostics and Health Management (P.H.M.), Health Monitoring can be seen as the first step to manage the global health state of complex systems. Health Monitoring of industrial systems focuses on accurately describing the health state of a system, using several equipment indicators. However, managers and maintainers have to make decisions. Such decisions can be hard to make while watching all indicators of the system simultaneously. In order to ease the decision making process, a synthetic indicator, which represent the actual system's state, can be used. In this paper, we will present an approach for building an aggregated indicator characterizing the global health state of a system. This approach was implemented on the TELMA platform (integrated TELeMAintenance platform for research and education) which simulates an industrial process.