Plotting a pass / fail bar / axis

[boostjunkie]

This is a function I've wanted to do for a long time and don't know the correct name. Basically I would like to plot a line across an x/y graph similar to the x-axis, but have it be set at some value. I believe I have seen this done on bar and line charts (and / or xy scatters). For example if X is distance and Y is force, I'd like to plot a line across Y=25 as say a minimum passing value.

[Andy Pope]

There are various examples of adding dataum lines to charts here
http://www.andypope.info/charts/averageline.htm