A control chart indicates when your process is out of control and helps you
  identify the presence of special-cause variation. When special-cause variation
  is present, your process is not stable and corrective action is necessary. Use
  control charts to do the following: 
 
  - Demonstrate whether your process is stable and consistent over time. A
	 stable process is one that includes only common-cause variation and does not
	 have any out-of-control points. 
  
- Verify that your process is stable before you perform a capability
	 analysis. A capability analysis is only valid when performed on a stable
	 process. 
  
- Assess the effectiveness of a process change. With control charts, it is
	 easy to compare shifts in the process mean and changes in the process
	 variation. 
  
- Communicate the performance of your process during a specific period of
	 time. 
  
 You can use a capability analysis to determine whether a process is capable
  of producing output that meets customer requirements when the process is in
  statistical control. You can use a capability analysis to answer questions such
  as: 
 
  - Is the variability of a process low enough to consistently provide parts
	 that fall within the specification limits? 
  
- Is the proportion of defectives consistently less than 5% during a month?
	 
  
- Is a temperature curing process capable across multiple batches of the
	 product? 
  
- Does a process need to be shifted to operate within the specification
	 limits?