Upper Control Limit (note, different from USL): representing a 3 x Sigma upwards deviation from the mean value of a variable (see also LCL). For normally distributed output, 99.7% should fall between UCL and LCL.
When used on control charts, the “3sigma” level can be calculated from sample-to-sample values or batch-to-batch averages using a “magic number,” and is used to flag-up unexpected deviations.
Unexplained Variation (S)
Regression statistical output that shows the unexplained variation in the data. Se = sqrt((sum(yi-y_bar)^2)/(n-1))
A unit is any item that is produced or processed which is liable for measurement or evaluation against predetermined criteria or standards.
A random variable with a numerical value that is defined on a given sample space.