The polygraph process is not a technical one, but a psychological one. The point is not to detect a lie by "registering it" on the tool, its to create a situation where a person self-elects information because they believe the machine _could_ detect a lie. Its a huge dog-and-pony show, and the poly operators play it as a big game.

So, polys _do_ sort of work, but not in the way they are presented to the public.