Just posted this on my website.  Let me know if it helps;
http://thetechfirm.com/ethereal/ethereal.html
Regards
Tony Fortunato, Sr Network Specialist 
The Technology Firm 
www.thetechfirm.com
Getting things to work better - bit by bit- 
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From: Ana Maria Quintana Checa <anaquin351@xxxxxxxxxxx>
Date: Mon, 8 Oct 2007 10:16:53 +0000
Hi!
I want to get the throughput data instead of the througput graph for a TCP
Stream.I have saved the capture to CSV format and copy to an excel file.
Does anyone Know how can I calculate the throughput ,like WireShark  does?
Thanks
 
AnaQ.