Source for Super Effective x2 ?

In the "Pokemon Type Chart - Strength and Weakness" we can see that a Super Effective attack can be multiplicate by 2 or 4. Where did you found these numbers ?

In the "Pokemon Type Chart - Strength and Weakness" we can see that a Super Effective attack can be multiplicate by 2 or 4. Where did you found these numbers ?

In the "Pokemon Type Chart - Strength and Weakness" we can see that a Super Effective attack can be multiplicate by 2 or 4. Where did you found these numbers ?

In the "Pokemon Type Chart - Strength and Weakness" we can see that a Super Effective attack can be multiplicate by 2 or 4. Where did you found these numbers ?

In the "Pokemon Type Chart - Strength and Weakness" we can see that a Super Effective attack can be multiplicate by 2 or 4. Where did you found these numbers ?

In the "Pokemon Type Chart - Strength and Weakness" we can see that a Super Effective attack can be multiplicate by 2 or 4. Where did you found these numbers ?

In the "Pokemon Type Chart - Strength and Weakness" we can see that a Super Effective attack can be multiplicate by 2 or 4. Where did you found these numbers ?

In the "Pokemon Type Chart - Strength and Weakness" we can see that a Super Effective attack can be multiplicate by 2 or 4. Where did you found these numbers ?