Input: the yellow gear.
Its number of remained teeth Z1c = 2
Its number of teeth (teeth-completed) Z1 = 20
Its number of cut-off teeth Z1f = Z1 – Z1c = 18
Output: the green gear.
It has 14 tooth slots.
Its number of teeth (teeth-completed) Z2 = 21.
When the yellow makes 1 revolution, the green makes 1/7 revolution.