Cheapest way of making a perfect item!

The keyword here is average (or, being more exact, expected value). If you want to scroll an item perfect infinite times, this will be the cheapest way to do so. You might get lucky on one try and hit some 30%s in a row, making it easier to make the item perfect, but the calculator calculates the cheapest way of making that item on average.

This....is what I was trying to get at by "not always exact"
For all you know, you could /never/ get a perfect scrolled item. And then, at the same time, it could take you 5 minutes (cheapest possible) to get it. You never know.