Gauge R&R: how much variation is the gauge?
A gauge R&R study separates measurement error from real part-to-part variation, so you can tell whether a tolerance decision is trustworthy.
Rational subgroup
A sampling group designed so within-group variation represents the short-term variation being studied.
Samples might come consecutively from one machine or cavity while between-group differences expose changes over time. Mixing different streams inside every subgroup can conceal the changes of interest. Retain stream and time identity with raw data, and document how the within-subgroup variation estimate was obtained. See capability indices.
See also: Statistical process control (SPC) · Process capability
Use the concept: Sample mean & standard deviation calculator · Cp, Cpk, Pp & Ppk calculator · Downtime log template
In depth
Takt time vs cycle time vs lead time: calculate the right clock
A worked shift example separates customer pace, observed process speed and end-to-end delivery time, with practical checks before changing the line.
SMED changeover study: measure last good to first good
Use a time observation sheet to separate internal and external work, preserve safe setup steps, and verify a repeatable changeover improvement.