Google for Excel, COM, macro, ...
You shouldn't have any trouble finding sample code (probably in VB or VBA) to do what you want.
Alternately, any good book on advanced Excel or MS Office programming should have the info you're looking for.
Regards
Dave M.
You can also try recording a macro of the steps you take to manually produce the chart.
Record a macro making the chart full screen. Record a macro of it not full screen. What's different in the two? Apply that to your Ruby code.
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