Incremental tag/counter tag

I have a realtime OPC tag KWH_TOTAL, which I am storing in a Historical Transaction Group at a rate of 5minutes.

Then I have created another SQL Query tag ‘KWH_DAILY’ to look at the KWH_TOTAL from my previously created Transaction Group (SELECT LAST(KWH_TOTAL) FROM kwh_table;).

Lastly, I subtract the two in a an expression tag called KWH ( KWH_TOTAL - KWH_DAILY).

Now this KWH expression tag, I want this to be an incremental tag, rather than JUST the difference between the two Tags? How do I make this tag (or whatever approach) to have the KWH only count up, based on the subtraction?

I am not quite understanding what you want when you ask for this to be an incremental tag. (Coffee hasn’t kicked in yet.) Would you explain a bit further what you are after?