I have to apologise, I shouldn't have post the graph without me understanding what it does and how to read it first. I do everything on the run lately. I should slow down or stop posting.
So what that graph is, I finally understood myself
, it is what Lars said, the DAC captured in the third numeric field from the Arduino serial multiplied by 2E-12 which in Lars's example with a gain of 500 and 130ppb range is the correct Hz/bit but in my case with a gain of 120 and a range of about 546ppb iiiiisss not...
On top of that I didn't read that I should use t=4 so that graph is garbage...almost.
I will redo it when I find the time with the correct time constant and the correct multiplier which in my case is more like 8.33E-12.
Did I get it right this time Lars?