Abstract: A liquid-flow monitoring device (10) arranged to monitor the flow of liquid in a conduit. The device (10) comprises sampling means (20), processing means (30) and data storage means (40). The sampling means is arranged to receive data substantially continuously from a sensor (12) indicative of at least one variable sensed by the sensor (12) indicative of fluid flow in a conduit and to sample the data to produce a stream of sampled data. The processing means (30) is arranged to process the stream of sampled data to extract at least one sub-sampled stream therefrom, the sub-sampled stream comprising a plurality of data sets, each data set being a statistical subset of the stream of sampled data over a respective data-set period. The data storage means (40) is arranged to store the at least one sub-sampled stream.