Adding Secondary Y Axis Help

1) Choose any one of the existing data series. Through the "select data" dialog, change the y values for that series to be the average (kN) values (http://office.microsoft.com/en-us/ex...752.aspx?CTT=1).
2) Adding the secondary axis should be the easy part: (http://office.microsoft.com/en-us/ex...165.aspx?CTT=1). Format the series you just changed in 1 to be assigned to the secondary axis.
3) Now comes the real hard part of this sort of thing. Because the two axes will represent the same data in different units, formatting the two axes so the axis limits and major and minor units all match up. Excel does not have a good way (built in) to automatically "link" the two axes together. I usually do it manually. Manually fix the limits and divisions of each axis so that they are "equal".

3rd party graphing packages might make this easier. I know many have them will allow you to define a secondary axis as a linear function of the primary axis.

Another option would be to use Jon Peltier's "aribitrary axis" technique to create a "dummy axis" that you would be able to control from the spreadsheet.