Control Chart is a graphical tool used to determine process performance with time. These were developed by Walter A. Shewhart and hence are also known as Shewhart charts. These charts help determine whether the process is stable or not. If the process is stable, the process will only have inherent variation (Common Cause variation). The region of common cause variation is given by Control limits (Upper and Lower control limits). Any process variation outside these limits is considered as Special Cause Variation.
Pre-Control Chart is a tool used to quickly check the status of a process. It is a tool used to actively manage a process and is more commonly used for high capability processes. It divides the specification limits into 2 zones - Green and Yellow. Green zone is exactly in the middle of the Specification width. The boundaries of Green zone determines the Pro-Control Limits. Area outside the specification limits is considered as Red zone. Samples are picked and checked as to which zone they fall in and depending on which zone the units fall in, one of the following decisions is taken
1. Continue running the process
2. Stop the process and fix it
Pre-Control Chart is typically used by shop floor workers / machinists to determine if some action is required on the process or not.
An application oriented question on the topic along with responses can be seen below. The best answer was provided by Bheemannadora Sappa on 13th September 2018.