How to create an Engineering Graph with two X-axis and a single Y axis

Hi,

I need to create a graph with a 2 x axis and a single y axis. For example:
Pressure ( PSIA) Solubility (mol %) Velocity (m/s)
200 0.024 1
300 0.036 1.2
400 0.041 1.8

I need the two x axis to be pressure and solubility and the y axis to be velocity, with the data being demonstrated by a single plot (I have only managed it with two plots which does not demonstrate solubility's relationship to pressure ).

For example at a pressure of 200 PSIA (lower x-axis) and solubility of 0.024 mol % (upper x-axis) velocity was found to be 1 m/s.

Your help will be greatly appreciated.

Many Thanks in advance

Preface by saying, I don't know where to find these commands in the newer version of Excel. The Help system should be able to help you find the commands -- if you get stuck, post here and someone with 2007/2010 will be able to tell you where the commands are. I will also add that this is a general approach. There are details you haven't given that make it difficult to give a specific solution.
1) In Excel, to get secondary axes, you have to assign at least one data series to the secondary axis system. Depending on how this spreadsheet is going to be used going forward, it might be as simple as assigning one of the two existing series to the secondary axes, or you may want to create a third "dummy" series to assign to the secondary axes.
2) By default, when you first assign a data series to the secondary axes, Excel displays the secondary Y axis only, and uses the primary X axis. You next need to go into the dialog that controls which axes Excel displays to tell it to hide the secondary Y axis (assuming you feel it is necessary to hide the secondary Y axis) and display the secondary x axis.

That is a basic description of how to get secondary axes in an Excel scatter plot. I think there must be more to the question because this:

For example at a pressure of 200 PSIA (lower x-axis) and solubility of 0.024 mol % (upper x-axis) velocity was found to be 1 m/s.

is not going to work as you've described it. At this point, the problem is less about Excel and more about the engineering -- understanding how the three variables are inter-related and how generally to visualize that relationship.

Perhaps there is a simple relationship (Henry's law???) between P and solubility? Then you would go into the secondary axis formatting dialog and modify the max/min/major/minor parameters so that the primary and secondary x axes "line up" as they should. Or perhaps one would be better off with something completely different (like a contour plot) for showing the relationship between these three variables.