When determining the upper and lower control limits for X-bar charts, and the process standard deviation is not known, factors from a table and the ______ are used to determine the UCL and LCL values.
A) X-bar
B) Range
C) Average range
D) sample standard deviation

Question

Quizplus · Accepted Answer

When the process standard deviation is not known, the average range (R-bar) is used along with factors from a table to determine the upper and lower control limits (UCL and LCL) for X-bar charts. This method relies on the range within samples to estimate the process variability.

When Determining the Upper and Lower Control Limits for X-Bar