Original author here. It's actually a method to convert from the index of an inventory hotkey slot into the keystroke used to access it -- there were ten hotke

Original author here. It's actually a method to convert from the index of an inventory hotkey slot into the keystroke used to access it -- there were ten hotkey slots, which were numbered 1–9 and 0 at the end. But I like all the other interesting interpretations here :P (They all assume way more knowledge than I had at the time.)