Here we have Statistical Process Control chart created using d3 (see https://en.wikipedia.org/wiki/Statistical_process_control). The chart uses statistical summaries of the data to define whether fluctuations are caused by random variance or from some external influence causing a change in behaviour. In the latter case, a data point is considered a 'signal' and the process is considered 'out of control'. A more permanent change to the data may result in a process break being inserted, and a new process starts. SPC charts are common in manufacturing, but here we look at crimes per month in the West Midlands region of the UK.
