Seems simple but can't figure it out - just trying to add in a straight, constant line at Y=0 for a waterfall chart.

Can anyone give a quick summary of which options I need to select to do that?

I have a waterfall chart with data points ranging from 80,000 to -50,000 and just want a horizontal line at 0 on the Y-Axis so it's easy to see that point instead of having an awkward gap between the data bars.