| Class Vocabulary | |
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attribute data
| 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
| 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
| The horizontal line on a control chart that represents the average for a process. |
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common cause
| 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
| 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
| 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
| An organization or individual that receives a product or service from the company. |
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grand average
| The average of sample averages. The grand average is the centerline on an X bar chart. |
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internal customer
| A department or individual within the company that relies on others to satisfy the external customer. |
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key quality characteristic
| 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
| A control limit indicating the boundary for the minimum permissible values. |
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micrometer
| 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
| Variation resulting from sources that are normal and expected. Natural variation is predictable over time. |
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normal distribution
| 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
| The control chart that tracks the percentage of nonconforming items. A P chart is used with attribute data. |
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process capability
| The total range of variation within a process, including common and special causes. |
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process control
| The range of variation within a process after special causes have been eliminated. |
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processes
| 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
| 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
| The control chart that tracks sample ranges over time. An R chart is used with variable data. |
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sigma
| A unit of standard deviation indicating the degree of spread within a set of measurements. |
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special cause
| 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
| 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
| The science of collecting, summarizing, and analyzing numerical data. Statistics makes it possible to predict the likelihood of events. |
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tolerance
| A blueprint specification indicating an unwanted but acceptable deviation from a given dimension. |
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unnatural variation
| 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
| A control limit indicating the boundary for the maximum permissible values. |
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variable data
| Data that contains a range of quantities. Most measurements yield variable data. |
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variation
| A difference between two or more similar things. |