These were thin books, printed on sturdy paper in full color, with white plastic spiral binding so they could be turned all the way back. The left pages were a quiz or puzzle, and the right pages were a short essay on the subject of the quiz in case you didn't know and wanted to look it up- but if you just wanted to test yourself, you could fold the book back instead.
They were associated with this little black plastic frame, the gimmick of the book. It was the "DECODER", as labeled in gold ink at the top. It was mostly rectangular, with dials for wheels sticking out of each side- five left, five right- and turning the dials caused a circle, square, or triangle to appear in a window (keep turning to get the one you want). Each one of those windows was next to a larger square window cut through the entire thing, resulting in this little pattern of ten zig-zag holes through it.
The quizzes were 3-way multiple choice (for the most part, there were some alternate formats), and the answers corresponded to a circle, a square, or a triangle; to answer the questions, you turned the dial for that question number until its window showed the shape for the answer you wanted. Once you'd tried all ten, you checked your work- there was this cloud of the answer shapes over a thick black line with an arrow on it; you lined up the bottom of the Decoder along the line, and made the arrows point to each other, and the shapes that showed through the window were all the correct answers and you could compare them to yours.
I've forgotten the name!
Does anybody other than me remember them?
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