Measuring-device-external display and evaluation unit, which is a mobile PC, a tablet, a smartphone or a wearable, comprising a slave pointer, configured to calculate a process variable, comprising: a computing unit, configured to approximately calculate a past temporal progression of the value of the process variable from process measurement data of a measuring device; calculate the current value of the process variable from the past temporal progression; wherein the computing unit is further configured to compare the calculated current value of the process variable with a current value of the process variable derived from current process measurement data; wherein the computing unit is further configured to instruct the measuring device to transmit process measurement data to an external receiver via energy-efficient long-range communication or short-range communication when the calculated current value deviates from the current value derived from current process measurement data by more than a predetermined threshold value; wherein the computing unit is arranged not to instruct the measuring device to transmit process measurement data to the external receiver if the calculated current value of the process measurement variable deviates from the current value of the process measurement variable, which is attributable to the current process measurement data, by less than a predetermined threshold value; wherein the computing unit is further configured not to instruct the measuring device to transmit process measurement data to the external receiver when the calculated current value deviates from the current value derived from current process measurement data by less than the predetermined threshold value. a computing unit, configured to approximately calculate a past temporal progression of the value of the process variable from process measurement data of a measuring device; calculate the current value of the process variable from the past temporal progression; approximately calculate a past temporal progression of the value of the process variable from process measurement data of a measuring device; calculate the current value of the process variable from the past temporal progression; wherein the computing unit is further configured to compare the calculated current value of the process variable with a current value of the process variable derived from current process measurement data; wherein the computing unit is further configured to instruct the measuring device to transmit process measurement data to an external receiver via energy-efficient long-range communication or short-range communication when the calculated current value deviates from the current value derived from current process measurement data by more than a predetermined threshold value; wherein the computing unit is arranged not to instruct the measuring device to transmit process measurement data to the external receiver if the calculated current value of the process measurement variable deviates from the current value of the process measurement variable, which is attributable to the current process measurement data, by less than a predetermined threshold value; wherein the computing unit is further configured not to instruct the measuring device to transmit process measurement data to the external receiver when the calculated current value deviates from the current value derived from current process measurement data by less than the predetermined threshold value.