Easy chart not Trending.. The whole line is moved when the value change

I have an easy chart on a process that is acting weird. When a value change, instead of trending, the whole trend lines move up or down accordingly with the value. No mather the time i select in realtime, it always display straight lines instead of trends. Same thing in historical mode.

How is the pen configured? Is there history being saved for that tag? Or are you just grabbing the live value only?

Each tag are historised

In fact it was working then it stopped working a week ago or so…

Ok Problem solved… for now… Not enough space on SQL express server. I deleted old databases and set the pruning at 6 month.