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attribute data
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Data that represents the absence or presence of characteristics. Go/no-go gaging or the presence/absence of a component yield attribute data.
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bell-shaped curve
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A graph of variable data characterized by a high center, tapered sides, and bell-flared edges. A bell-shaped curve reflects conditions that exhibit natural variation.
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centerline
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The horizontal line on a control chart that represents the average for a process.
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common cause
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A source of variation that is normal and expected. Common causes are predictable over time and yield a normal distribution.
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control chart
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A graph used during SPC efforts that charts data and provides a picture of how a process is performing over time.
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control limit
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A horizontal line on a control chart that represents a boundary for a process. If the process strays beyond a control limit, it is out of control.
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external customer
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An organization or individual that receives a product or service from the company.
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grand average
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The average of sample averages. The grand average is the centerline on an X bar chart.
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internal customer
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A department or individual within the company that relies on others to satisfy the external customer.
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key quality characteristic
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A measurable characteristic of a product that greatly impacts customer satisfaction. Key quality characteristics are the focus of SPC efforts.
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lower control limit
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A control limit indicating the boundary for the minimum permissible values.
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micrometer
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A U-shaped measuring instrument with a threaded spindle that slowly advances toward a small anvil. Micrometers are available in numerous types for measuring assorted dimensions and features.
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natural variation
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Variation resulting from sources that are normal and expected. Natural variation is predictable over time.
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normal distribution
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Variable data that clusters about an average and is symmetrical. When graphed, a normal distribution appears as a bell-shaped curve. In-control processes yield a normal distribution.
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P chart
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The control chart that tracks the percentage of nonconforming items. A P chart is used with attribute data.
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process capability
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The total range of variation within a process, including common and special causes.
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process control
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The range of variation within a process after special causes have been eliminated.
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processes
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A set of activities that uses resources to transform inputs into outputs. Essentially, a process describes the way "things get done."
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quality
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The satisfaction of customer requirements. Quality products conform to specifications, are free of defects, and meet the requirements of its anticipated use.
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R chart
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The control chart that tracks sample ranges over time. An R chart is used with variable data.
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sigma
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A unit of standard deviation indicating the degree of spread within a set of measurements.
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special cause
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A source of variation that causes a fundamental change in a process. Special causes distort a normal distribution and are undesirable.
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statistical process control
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The use of statistics and control charts to measure key quality characteristics and control how the related process behaves. SPC separates special causes of variation from common causes.
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statistics
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The science of collecting, summarizing, and analyzing numerical data. Statistics makes it possible to predict the likelihood of events.
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tolerance
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A blueprint specification indicating an unwanted but acceptable deviation from a given dimension.
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unnatural variation
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Variation resulting from one or more sources that involve a fundamental change in a process. Unnatural variation is undesirable.
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upper control limit
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A control limit indicating the boundary for the maximum permissible values.
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variable data
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Data that contains a range of quantities. Most measurements yield variable data.
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variation
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A difference between two or more similar things.
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