Control charts help to determine whether or not a process is stable or has predictable performance. This function of control charts is achieved through the graphical display of results over time to determine whether differences in the results are created by random variations or are unusual events. In a manufacturing environment, such charts are used to track repetitive actions such as manufactured lots. In a project management environment, they can be used to monitor processes such as cost and schedule variances, number requirements, and errors in project documents.