SPC Concept

• All processes vary.
• The aim of SPC is to minimise variation.
• Variation is expressed in "sample standard deviations" (SD)
• SD is a mathematical term, based on probability theory.
• Consider the process of driving a car along a dry, straight, level road.
• Look at your hands on the steering wheel - they move as you make slight adjustments.

If you draw a graph of the movements you will have a "normal distribution curve"

In a normal distribution, most of the time your hands are in the middle

(In the secret language of SPC the "middle" is called the "average" or "mean" or "x-bar")

But sometimes your hands are a little to the left, at other times they're a little to the right

And on rare occasions they're on the extreme left or extreme right.


Taken from www.iso9001help.co.uk

SPC - statistical process control

What is SPC:

The method of SPC was discovered by Walter Shewhart during the 1920s

SPC is an informative inspection technique that uses control charts to determine when shifts or changes are likely to have occurred in a process.

• Makes no assumptions on performance
• Simple graphical representation of current process performance
• Helps to understand the potential of achieving targets
• Focuses on detecting and monitoring process improvement