Drop in Level Totalizer

Hey guys, I'm using ABB Freelance 2000 and need to totalize by drop in tank level. I currently use the integrate function to totalize flow and this works well, but am having trouble convertly a drop in tank level to a flow in real time. Does someone have experience doing this?

It will be hard to get a real time reading I think.
Perhaps if you take the difference in level minute to minute then add say the last 10 readings and divide by 10 to give you a fairly smooth result you might get something usable. Every time you take a new reading discard the oldest. First In, First Out.
I have used this method with a weigh scale to indicate very small flows of slurry