@roar
Even though, my knowledge in the domain is very poor, i saw your topic and i couldn't avoid making the link with a formula i've seen recently about reproducing sort of chaos, it is :
X=4.x(1-x) with x between 0 and 1, both excluded, and replacing x by the results in the next operation, and
so on, as a mathematical series.
Not sure you can reproduce a 100% random chart, when even this exemple has his rule, it would give something crazy. I think youll be able to use this pretty simple equation in excel without any problem.