Incrementation by Seven

STEP 1

Just count the numbers on the cycle, e.g. 0-7-4-1-8-5-2-9-6-3-0-7-4-1- 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.

This is maybe the most difficult routine to master.

BEGINNER	SLOW
MEDIUM	FAST