Hi, just to let you know that as a native speaker of EN, "calculus" is a very specific area of maths as both Tony and FX Fraipont point out.
The word calculus is a word we hardly ever use in day to day life - indeed many English speakers would not understand the word! I studied calculus as part of my A-level maths course i.e. when I was 18 and I seem to remember my own parents had no idea what it was!
The book must be about calculus, which is why the daughter mentions it.
http://en.wikipedia.org/wiki/Calculus