I want to be able to add horizontal lines to my chart, in this case at 4% and
6% on the y-axis. The solutions I've seen so far suggest to add a series at
these points. The problem is that when I add a seires, my legend shows the
new series when I don't really want them to. Is there a really simple way
that I've overlooked so that I can just add a line at one y-value and all the
x values on the graph and not have it appearing in the legend?

Thanks