Need help finding a magic trick

I'm having trouble finding a trick I used to do. I'll explain a few details: you'd start with a totally pre-arranged deck, explain what the effect was about, and ask the spectator to cut a small packet of cards while the magician guessed how many there were. The spectator kept cutting, and the magician kept guessing. Then the magician would cut right to the middle, and the routine would go on from there. I don't remember any more; if anyone knows what routine I'm talking about, please drop a reply below. Cheers