Equa Pocket Puzzle

This unusual mechanical challenge was inspired by the design of an ancient scientific instrument called an astrolabe. Two crossed rings rotate within the tetrahedral frame but small metal tabs block their movement in certain directions. It may seem unlikely, but not only is it possible to unlink the rings and remove them from the frame, there are two different ways to do it. One solution unlocks both rings at once, and the other takes them out one at a time. A difficult problem even for advanced puzzlers.