Statistical process control: control charts that catch drift early
Apply SPC where it works — control chart selection, rational subgrouping, capability indices, and the reaction plans that turn charts into control.
Specification limits
Engineering or customer acceptance boundaries for a product characteristic.
Lower and upper specification limits describe allowable product values. They are requirements, not estimates of current process behavior. Do not replace them with control-chart limits when calculating capability. Record the approved specification revision with the result; the capability guide explains the distinction.
See also: Control limits · Process capability
Use the concept: Cp, Cpk, Pp & Ppk calculator · Downtime log template · MTBF, MTTR & availability calculator
In depth
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.
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.