# R-Bar – Range

Part of most of any statistical
process control plan. Range is the spread of the observations, *(subgroups)*,
using stratified sampling and
usually a random sampling plan.

It is calculated by subtracting the lowest
sample from the highest sample in the
observation set. R-Bar, is the average range of a set observations, *(subgroups)*.
This data is typically charted on a line control
chart with the center line being R-Bar, *(an average of the ranges)*,
and upper control limits and lower
control limits. *(see X-Bar
and Range, (R-Bar), Control Charts for a pictures and additional
information of these types of charts)*

Range measures the variability
of the process.

**N is the largest sample in the observation set**

n is the smallest in the observation set

###

### Example:

### Range1 – (.051 – .049) = 0.002

Range2 – (.052 – .049)= 0.003

### R-Bar = (Range1 + Range2) / 2 =
0.0025

R-Bar = 0.0025

For an example of a R-Bar charts see our ZeroRejects
features page. It makes doing six sigma
and statistical
process control charts easy and it only costs $150.00.