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The is a hole drilled in them slightly off center. If you ever get a chance to buy used casino cards, get corner cut, not drilled cards. The drilled hole cause the edges to raise and makes it hard to shuffle the cards. I'm a collector of junk, especially swag junk, so I've made these into my practice cards for counting cards for black jack.
A single deck will have a full count of zero. When I received these cards, I had never managed to properly count a deck to get zero. I'm always off by one or two. So now a week later I'm getting a count of zero on better than half of my attempts. As I have read, counting cards is harder than it looks.
I now count a deck in about one minute, twenty seconds with reasonable accuracy. I sometimes can count the deck in one minute nine seconds. My goal is to count the deck in 25 seconds. Once I can correctly count the deck 50 times in 25 seconds, I'll feel I'm ready for the next step in training.
For now, I'll stick to poker.