Alert and action level

Why alert and action level calculate??
Why not same limit consider as per guidelines given?

Hello Tushar,

The main idea behind this is so that you have ways to be preventive, instead of reactive, by monitoring your process, understanding its variation, and know when your process is out of statistical control or if it has gotten to a point where you must take actions before it becomes out of specification.

Alert level: generally, you woud want this to be representative of the natural variation of the process, meaning that any vlaue outside of this level is so unlikely to happend that it is very probable that it was caused due to an uncontrolled source of variation worth investigating

Action level: this is a bit trickier, but you would want this to be located at a value between alert and specification, that you know you have enough “space” to act before it becomes an out of specification, but without “overreacting” when it is not necesary.