What does HP-41 <<"FFD" XROM "HN" STO b>> do?

[rprosperi]

@Joe - Now that it's clear what this little note is for, does it appear on a page/location in the SQRG that corresponds with the ROM version topic? It's unlikely you would have written that on just some random place in the booklet, but OTOH, it is so densely packed with details, that there is not a whole lot of free whitespace for notes. Just curious...