January 7, 2006
It's a nine-square by nine-square grid. The grid is subdivided into nine three-by-three grids. Each column has the numbers 1-9, with no repeats (only one "2", only one "4", and so on). Each row has the numbers 1-9. Each three-by-three grid has the numbers 1-9. You do not need to guess what number goes where; logic and the process of elimination are sufficient to figure it out. But it's maddeningly challenging and addictive. I like the website above (and I've added the link to the sidebar) because you can check as you go to see if you've made a mistake. Enjoy!