Incrementation by Nine

STEP 1

Just count the numbers on the cycle, e.g. 0-9-8-7-6-5-4-3-2-1-0-9-8-7- etc. Know this by heart before you do step 2.

STEP 2

Do first as beginner, then migrate to slow, then medium, and then fast. Keep up in counting along with the graphic progression.
Remember, a 0 means any number that ends in a zero, like 10, or 40 , or 2430.

BEGINNER	SLOW
MEDIUM	FAST