Use Rules to Retrieve Previous Value

Now it is possible to look up the previous value of a field using the automation rules. When you add _was at the end of a field name, the expression will retrieve the field’s previous value.

Below is a simple example that shows how this can be used in a rule:

Note that the Condition includes and old_subject, as otherwise the condition would be met when the task is created. That’s because when the task is created, the status is updated from nothing to a value (thus triggering the rule) and the subject is also updated from nothing to something (thus causing the condition to be met).
By including and old_subject in the condition, the condition is not be met when the old_subject does not exist (and therefore is not true).