(eng): Pervasive uncertainty of information which affects to some extent functionality of every control and information system concerns naturally the condition monitoring systems as well. Uncertainty can practically be disregarded when monitoring a single component, but it should be taken into account when compounding extensive amount of information within a hierarchical diagnostic system. When using uncertain informa- tion for expression of inner system’s relations, probabilistic and namely subjective logic may do a good turn. However, the key problem remains how to quantify the uncertainty on the lowermost level of the monitoring system. The paper introduces several solutions based on inspection of either a single measured signal or a couple of correlated signals.