Hi,
Following on from Bernard, once you've found the x and y values for your
sample, just plot them as a new series on the chart. You can also add x and
y error bars linking the point with each axis if you want to do it like in
the "old days" when we used graph paper.
Obviously, it looks better if you've removed the lines between the data
points and added a suitably formatted (preferably linear)trendline to the
chart. If you've done the calculations properly, you should see your new
sample point sitting on the trendline.
Don't be tempted to apply some higher order polynomial trendline just
because it looks to fit the data better.

Dave

url:http://www.ureader.com/msg/10297359.aspx