Unlinking a source sets the Valid To date for that Source Linkage to the current time such that the historical data for the DeltaV source is no longer related to batches that use the Batch Executive source. This does not prohibit the Source Linkage from being used by users or applications working with batches that started between the Valid From: and Valid to: times, only batches that were started after the sources were unlinked. Unlinked sources are recorded by the Batch Historian and appear in the Historical Links panes on the bottom right-hand side of the dialog along with the time period for which they were valid. This allows users to review the Source Linkages that were in use at any particular point in time.