When determining process capability, we look at the $($normal$)$ distribution of the production output $($with mean mu and standard deviation sigma$)$ and compare it to the specification range. In its strict sense, the six$-$sigma designation refers to:

Group of answer choices

The points $($mu $+3$ sigma$)$ and $($mu $-3$ sigma$)$ must fall within the specification range, but the points $($mu $+6$ sigma$)$ and $($mu $-6$ sigma$)$ need not fall within the specification limits$.$

The points $($mu $+3$ sigma$)$ and $($mu $-3$ sigma$)$ must fall within the specification range, but the points $($mu $+6$ sigma$)$ and $($mu $-6$ sigma$)$ need not fall within the control limits$.$

The points $($mu $+6$ sigma$)$ and $($mu $-6$ sigma$)$ must fall within the specification limits$.$

The points $($mu $+6$ sigma$)$ and $($mu $-6$ sigma$)$ must fall within the control limits$.$