The music is notated as if there had been no detuning so that you can use the natural finger positions. (For example, a note that is notated as a C would actually sound as a B.) The trade-off is that it makes some of the intervals look wrong, but you do get used to it.

Bach's 5th cello suite also uses this technique where the A string is tuned down to a G. (The technical term is "scordatura.")