Shewhart individuals control chart

In statistical process control, the individual/moving-range chart is a control chart for variables data that uses individual measurements of a quality characteristic.

When to Use?
 * 1) In situations where opportunities to obtain data are limited, such as low production volume or testing.
 * 2) Sampling sizes greater than 1 simply do not apply, such as when sampling form homogeneous batches (eg., heat treating), or when samples have very small short-term variation. (e.g., sheet metal stamping), or for business processes (e.g., performance measures).

Why do we USE?
 * 1) To display and manage variation in process output over time.
 * 2) To identify when a process changes.
 * 3) To provide a basis for improvement.
 * 4) To distinguish special from common causes of variation ( that is, when to correct sporadic problems or when to change the process).
 * 5) To help assign causes of variation.