Originally Posted by
Roelof
Nice! Which program is that?
With a simple straight calculation I was not far off
You where quite close!
I used this (you find it if you scroll down);
http://2.3liter.com/Calc2.htm 
I´m not sure how accurate it is, but for a quick calculation I think it´s accurate enough.
For more in-depth analysis I use other programs.