Calculating PPC ROI

I have put this up so I can reference it too. It is is response to something I read about some guys who were talking about ROAS.

PPC ROI I have found that ROAS is an awful indicator for performance. Try using the pure ROI equation. Calculating the ROAS is a basic equation of revenue/cost.
To calculate PPC ROI:

First get the contribution: (Revenue X Margin) - Ad Cost = Contribution
So using the numbers from the example with a presumed 50% margin:
(1574 X .50%)=787)) Then - 787-1525=-738
contribution is -738

The to calculate PPC ROI Use: Contribution/Cost

-738/1525= -48% ROI

Yeah that is awful...