I have operators who are inputting data and that gets written to a tag which has history on and set to "sample on change". They do this once a day but the problem is, if they enter the wrong value even after confirmation boxes etc... there isn't a way to undo change. Is there a way to remove the last tag change from tag history?
Yes. You have to go into the database itself and delete the record that was logged when that tag change occurred. There is no first party way to do it from the gateway webpage or the designer.
You could script it as well by running a DELETE query. Best to avoid that if you don't know what you're doing though, else you may delete more than you wanted....
... and you have to figure out which partition you need to delete from. Typically partitioning is done by month.
Sounds fragile. Consider using an input form with unbound entry fields that has a "Save" button. And, perhaps, save to a custom table instead of relying on the historian.
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If they enter the wrong value, does that have any impact in the real or virtual world?
If they enter the wrong value, do they immediately change it again to the correct value?
Is the history log some sort of official system of record?
I am a strong proponent of immutable histories. Maybe there is a case for deleting the change from the history but I'd have to be convinced.
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