Spaced repetition algorithms Can someone tell me how the Super Memo spaced repetition algorithms (http://www.supermemo.com/english/algsm11.htm) were calculated?

How does someone go about designing algorithms like this?

Is there a particular branch of mathematics that deals with this type of issue? 

I understand the logic of the different variables and why they are included in the algorithm, but not how these elements are formed into a single unit. 

I'm interested in it and would like to do some reading on the subject. 

Thanks for any help
I do not know exactly how it is calculated, but some of the SuperMemo algorithms are open source. Also, I have used SuperMemo for about nine years and have memorized over 77,000 flashcards with a 95% accuracy. I don't know the exact calculations, but I do know that they work.
I do not know exactly how it is calculated, but some of the SuperMemo algorithms are open source. Also, I have used SuperMemo for about nine years and have memorized over 77,000 flashcards with a 95% accuracy. I don't know the exact calculations, but I do know that they work.