I like many other entrepreneurs found myself guilty of incorrectly calculating roi, luckily Fred Wilson has made a very easy to understand example so that i can have a simple understanding of what I am asking a vc to provide - and a clearer understanding of the risk they are taking and the return I can expect to provide back.
In his post here: http://www.avc.com/a_vc/2010/01/how-to-calculate-a-return-on-investment.html he shows how the roi is simply calculated.
the impressive thing was that when i opened the spreadsheet app there were several of us looking at the example, and there was an opportunity to chat. this is the new classroom for the self taught.
Looks like Fred has opened the door for many of us who read his blog to come together a bit, hopefully this will continue.