Recalculate Tag Values Manually

About this task

One instance when you might want to recalculate data would be after the Historian server restores a lost connection. During the period of connection loss, the collector buffers data. When the connection is restored, the buffered data is forwarded to the Historian Server.

When the buffered data arrives, the timestamps are earlier than the most recent calculation timestamp. Since the timestamp is earlier, polled calculations are not performed again with the new data unlike the unsolicited calculations. Hence, it is possible that calculations performed for tags during and after the connection loss might not be entirely accurate. Therefore, you can recalculate tag data for the time period during and after the connection loss. The recalculated data will use the most accurate values in calculations.
Note: You can still use manual recalculation without automatic recalculation by disabling the automatic recalculation feature. To disable the automatic recalculation, set the Max Recovery Time to 0 in the Configuration section of the Collector Maintenance page of the collector.


  1. Access Historian Administrator.
  2. On the Main page, in the Collectors section, double-click the collector whose tag values you want to recalculate. Alternatively, you can select Collectors, and then select the collector from the Collectors pane.
    The General section of the collector appears, displaying the properties of the collector.
  3. Select Recalculate.
    The Recalculate Tags For <collector name> window appears.

  4. Provide values as described in the following table.
    Field Description
    Start Time Enter the start date and time. Tag values calculated after this date and time will be recalculated.
    End Time Enter the end date and time. Tag values calculated until this date and time will be recalculated.
    Tags to Recalculate Specify whether you want to recalculate values for all the tags added in the collector or just the selected tags. If you select Recalculate Selected Tags Only, the Tag Name and Description fields are enabled.
    Tag Name and Description Enter the search criteria to filter out the tags whose values you want to recalculate. These fields are enabled only if you select Recalculate Selected Tags Only. After you select Browse, the search results appear in the Browse Results section.
  5. Select Recalculate.
    A message appears, asking you to confirm that you want to recalculate the data.
  6. Select OK.
    The tags values are recalculated.