Here's a small TI-86 program for twiddling Linux/UNIX permission bits and seeing both the symbolic and numeric results. The simple ones (750, 640, 755, etc.) are easy enough to do in one's head, but it can start to get a bit messy when setuid, setgid, and sticky get involved.
Articles in the Computers category
Generally, I don't trade in warez on this site, but for software that's pretty much abandoned, and the original company having vanished, I'm willing to make an exception.