The use of "precisely"

Question

There are various ways in which something can be wrong, but in this case, if you had to explain it, you'd probably say that it would be unfair to other users of the library who may be just as interested in the book as your friend is, but who consult it in the reference room, where anyone who needs it can find it. You may also feel that to let him take it would betray your employers, who are paying you precisely to keep this sort of thing from happening.

What does it all mean, Thomas Nagel, Chapter VII

I don't know the use of "precisely" in the context above. Which word does it modify? "paying" or "keep"?

Answer 1

It modifies 'to keep this sort of thing from happening'! Presumably the passage refers to illicit borrowing of library books. Library staff are employed for the specific purpose of controlling the loan of books and making sure that reference books don't leave the library.