This month we took the checker board at college. It is used for long multiplication.
I now have a slight problem, I'm totally hooked on it.
I don't actually own one, however I have been doing teacher training for a school and they will be paying me by materials. First material I have on my list is this and I will be expecting it very soon.
I was going to type up the presentation but luckily I found a detailed online presentation here which is a sample from the NAMC manuals.