A free online reference for statistical process control, process capability analysis, measurement systems analysis, control chart interpretation, and other quality metrics.
Don’t miss out! Book a demo of our specialized SPC software and unlock immediate improvements in your processes.
Tools for analyzing and interpreting data so that areas to improve become apparent.
(Learn more)
Consists of measurements of a characteristic, such as length, weight, density, time, or pressure.
Consists of defects per item (nonconformities) or the number of defective items (nonconforming). For example, the number of non-working parts in sample or the number of blemishes counted on an individual part.
Consists of a count of items or occurrences, such as the number of defective items, the number of scratches on a door panel, or how often a specific problem occurs.
Use this when other control charts are not effective to determine if your process is stable.
Answer “yes” or “no” to a series of questions about your control charts.
Follow these steps to interpret histograms.
A resource for data collection tools, including how to collect data, how much to collect, and how frequently to collect it.
A tool used to indicate how much data to collect and how often it should be collected.
A clear, concise, detailed definition of a measure.
Gage R&R refers to testing the repeatability and reproducibility of the measurement system.
Process performance indices use sigma of the individuals.
Pp for one-sided specifications
If you are using one sided specifications, use the following formulas to determine the Cp:
Upper specification
Lower specification
Where:
Zmin is the smaller of Zupper and Zlower.
Using sigma of the individuals:
Capability indices use estimated sigma.
Cp for one-sided specifications
Using estimated sigma:
T = specification target (nominal)
Xi = a given individual reading of ” i ”
n = total number of individual readings
= symbol for summation
The t-chart formula:
The g-chart formula:
The c-chart formula (for number of nonconformities, from subgroups of a constant size):
The u-chart formula (for number of nonconformities from subgroups that can vary in size):
The p formula (for the proportion of nonconforming units from subgroups that can vary in size):
To calculate control limits for the p-chart: