It is a way of reading signals in charts.

It is a mental process of questions and pattern recognition.

Out of control does not always mean trouble.

Basic rules for recognizing unstable conditions:

• Any point outside control limits.
  • Points outside of control limits is called special cause variation.
  • Points within control limits is called normal process variation.
• Run of seven points.
  • Above or below center line.
  • In a row moving up or down.
• Nonrandom patterns.
  • Too close to average.
  • Too far from average (2 of 3 points in Zone A; 4 out of five in Zone B).
  • Cycles.