Thanks for the fast answer! That’s an interesting trick, but a bit clumsy, and the results are unusable in most situations: look at the gaps when the points around the pos/neg flips are not close to zero:
You can introduce extra dataPoints at the beginning and at the end of the dataSeries with y-value 0 and x-value between the last dataPoint of previous dataSeries and first dataPoint of the next dataSeries.
Not really. I cannot invent A new date between two adjacent dates can I? And even if I could, it would be even more clumsy. Should be an standard feature I think. Is it easier if I use bars instead of splines?
Yes, column/bar chart should work fine without introducing new dataPoint in this scenario. However, you need to set dataPoint color based on its value, whether negative or positive. Please take a look at this jsfiddle.