An optical monitor that generates a signal indicative of at least two optical properties of an input optical signal. The generator is supplied with liquid by an electric pump, and the flow rate of the steam thus generated is higher than 5 gmin, and preferably of between 10 gmin and 60 gmin. In parallel, queries are performed on the time series data on each of the selected ones of the plurality of separate data storage devices to obtain a plurality of results. During a read operation, if the gap length does not comport with the additional data, then an error is assumed. Thereby, the coupling force between the trailing arms and the torsion beam made of different materials can be improved.