It seems that my best shot is,
- Create a batch-number dataset with (t_stamp, number) pairs. Number is in sequence 1, 2, 3, etc.
- Create another y-axis. I set the axis range to very large numbers so that the difference in vertical position of my batch numbers is not discernable. In my case I made it
max : 1000andmin : -10000. This forces the zero line above the top of my other charts. - Add another series and set it to line. Bind it to the batch-number dataset.