The original Slate of Mind, given that name by U.F. Grant c.1947, was essentially a card trick that could pass over into the realm of a mental prediction. His version and subsequent versions up until recently all used gimmicked cards and were self-contained and easy to do. The basic effect is that six (or so) cards are placed around a slate (or whiteboard or writing pad). The magician writes down a prediction on the slate (etc.). One of the cards is then chosen and placed at the top of the board. The board is then turned around to reveal that the card chosen matches the magician's earlier prediction, while none of the other cards match.

I have recently published a history of the evolution of this effect called "Evolutionary Slate of Mind" in the Wizards' Journal #17 (on my site), along with my own version which uses no gimmicks whatsoever (all may be examined, as they say) and one easy-peazy sleight known to even the most elementary students of card magic. Some of you may find it of interest.