Hi,
I haven't looked at the refernces you were given, but here is one appoach.
In your data area add one addition series with all the cells referencing a
single cell somewhere else say A1. Then all the formulas for the new series
are =$A$1. In A1 enter the value you want the line to have. Select the
series in the spreadsheet and copy it. Right-click the Chart Area and choose
Paste. Select the new bar and choose Chart, Chart Type, Line and pick the
first sub type. You can easily move the line by entering a new value in A1.
If this helps, please click the Yes button.
