How does a program find the current File number?

[brickviking Profile]

I've been working on my fx-9750GII with my Grocery program a bit (download link), and decided I want to know how to find what currently-assigned File number the calculator has assigned. Now I can look it up in Stat's Setup screen when I'm running the Stat application, but how do I find the currently-assigned File from within a BASIC program? I haven't seen that in any manual I've looked at, only how to set it. It'd be a bit awkward to have the user start off with File4 selected, and she starts my program, only to be bumped back to File1 at the end, not File4.

(Post 18)