Sigma chart
properties | Configuring a Sigma chart |
Sigma chart
calculations

The Sigma chart, also referred to as an S chart, shows the Sigma
(standard deviation) of subgrouped data. The sigma chart shows how
the data is spread and is used to study system variability. The
spread of a process is how far data points are distributed away
from the mean (center). Standard deviation uses each individual
reading to calculate variability; therefore, Sigma is a more
efficient indicator of process variability than Range, especially
with larger sample sizes.

In the following Sigma chart example, the subgroup size for the
sample data is 5. The sigma (standard deviation) of each subgroup
is plotted on the chart. The control limits (shown on the chart as
UCL, CL, LCL, WL1, and WL2) are set according to the data and a
sigma limit of 3.

### See Also