Visualisation method for process data (x, x*, Pi) by a visualisation system, - wherein an industrial technical installation is controlled and monitored by a process control system, - wherein the process control system at acquisition points in time in each case acquires the process data (x, x*, Pi) and the process data (x, x*, Pi) that is acquired is archived in the sense of a history, - wherein, owing to the selection of an item of process data (x, x*, Pi) and the specification of an associated display period of time by at least one operator of the process control system for the predetermined display period of time, the visualisation system requests the history of the selected item of process data (x, x*, Pi) and outputs the associated temporal curve as a graphic to the at least one operator, - wherein the graphic comprises a number of process data points, characterised in that - the visualisation system determines the respective process data point with reference to the values of the selected item of process data (x, x*, Pi) of a respective acquisition period of time that is characteristic of the respective process data point, wherein the acquisition period of time comprises a plurality of acquisition points in time, - the respective process data point is a mean value or a median value of the process data (x, x*, Pi) of the respective acquisition period of time, - the visualisation system also determines the minimum (Min) and/or the maximum (Max) of the values of the selected item of process data (x, x*, Pi) for the respective process data point during the respective acquisition period of time and - the visualisation system checks whether the minimum that is determined for the respective process data point is below a predetermined minimum value and/or the maximum (Max) that is determined exceeds a predetermined maximum value and for the case that one or both checks are positive, the visualisation system displays a secondary alarm (A') together with the respective process data point, wherein a secondary alarm (A') represents an alarm that is not set by the process control system but rather is set by the visualisation system. - wherein an industrial technical installation is controlled and monitored by a process control system, - wherein the process control system at acquisition points in time in each case acquires the process data (x, x*, Pi) and the process data (x, x*, Pi) that is acquired is archived in the sense of a history, - wherein, owing to the selection of an item of process data (x, x*, Pi) and the specification of an associated display period of time by at least one operator of the process control system for the predetermined display period of time, the visualisation system requests the history of the selected item of process data (x, x*, Pi) and outputs the associated temporal curve as a graphic to the at least one operator, - wherein the graphic comprises a number of process data points, characterised in that - the visualisation system determines the respective process data point with reference to the values of the selected item of process data (x, x*, Pi) of a respective acquisition period of time that is characteristic of the respective process data point, wherein the acquisition period of time comprises a plurality of acquisition points in time, - the respective process data point is a mean value or a median value of the process data (x, x*, Pi) of the respective acquisition period of time, - the visualisation system also determines the minimum (Min) and/or the maximum (Max) of the values of the selected item of process data (x, x*, Pi) for the respective process data point during the respective acquisition period of time and - the visualisation system checks whether the minimum that is determined for the respective process data point is below a predetermined minimum value and/or the maximum (Max) that is determined exceeds a predetermined maximum value and for the case that one or both checks are positive, the visualisation system displays a secondary alarm (A') together with the respective process data point, wherein a secondary alarm (A') represents an alarm that is not set by the process control system but rather is set by the visualisation system.