There are 144 squares on this table. You will not need to learn 144 separate things. Half of the table is a mirror of the other half, and most of what is left follows a rule you can pick up in a minute. Each table has its own material, brass for the fives, bark for the nines, so your eye can help your memory. Tap any square to begin.
How this works
Explore. Tap a square to see the fact, a picture of it, and the rule behind it. Tap a number down the left side to meet that whole table.
Lenses. Fold the table in half to see how much of it is mirror. Or show only the 21 squares that need real practice.
Hide the answers. Tap a square, work it out in your head, then tap it again to check.
Practice. Answer questions on a keypad. Each right answer polishes a square. After three, it shines. A wrong answer takes one polish away and brings the question back soon. Your progress stays on this device.