Graphing the Delta

W0w seems like it's been some time since I've had to ask a question.

I'm looking to trend/graph the delta. I will have an ever increasing
counter that I would like to grab the delta and graph that. (for
trending).

So I really want to be able to subtract the current result from the
previous result and having a hard time working that out. What am I
missing?

Thanks
Tory

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