How to Read X and Y value of any point on a chart in excel 2007

[anhphung]

I created a line chart. Then i want to read X value of Y = 50 on that line. In excel 2003 i heard that we can do that by creat a dummy point then move it anywhere we want to read X,Y value. But in 2007 i can't move any point . Please help me with this. Many thanks (sorry my english is not very well)

 

[tweedle]

MS has a sample for this.
http://support.microsoft.com/kb/300643
I tried it in X2007 and it flies.