Add x=y line to scatter plot

I have created a scatter plot with 3 data points, no line connecting them. Now what I need to do is add an x=y line to the scatter plot. I cannot figure out how to make the plot display data in two different formats. A trend line will not work because it must be x=y. Here is a link to the file in my dropbox if it helps anyone to look at it.

Originally Posted by shg

Plot another series with two points -- say, {0,0}, and {10,10}

Yes that part is easy but it will not be a line just two points since the first series is just points and not a line.

Originally Posted by shg

Any series can have any combination (neither, either, or both) of markers and lines. Right-click the series on the chart, format series ....

Thank you that did it. I was trying to change the series in the chart tools which changes everything. Very much appreciate it!