If the reference line is based on a measure, a single reference line can be added with a scope of Per Pane and the aggregation of the measure. If each reference line will need its own constant, one way would be to add a reference line for each quarter and use the label to name which quarter it represents.
I'm trying to do the latter, but I don't know how to add an individual reference line for each quarter so that the reference line does not cover the entire graph. Ideally I would like to have a single reference line only hovering over each of the bars that represent each quarter.
It sounds like your revenue target could work as a simple second line mark on a synchronized dual axis. Or do you require the targets for each quarter to be distinct lines from one another?
It would also help if you could attach a sample workbook illustrating your problem.