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Glossary - U
 

U Chart: Count-per-unit chart.

u
Chart -
 (1) A chart used to monitor the number of defects in sequential production lots. (2) An attributes control chart that is used to monitor the number of nonconformities per unit, such as defects per item. The subgroup size may vary.

Undercontrol - Not reacting to a set of data when the data is showing an issue or problem. For example, in a control chart, it would be ignoring a special cause of variation.

Undeveloped Events - A term used in fault tree analysis. Undeveloped events are faults that do not have a significant consequence or are not expanded because there is not sufficient information available.  

Unified Theory for Services Management -
 A set of propositions relative to managing services.

Uniform Distribution - A distribution, when drawn as a histogram, has each bar at a similar frequency.

Unit -
An object for which a measurement or observation can be made; commonly used in the sense of a “unit of product,” the entity of product inspected to determine whether it is defective or nondefective.

Unstable System - A system that contains special and common causes of variation; this system is also said to be out of control. An unstable system is unpredictable.

Upper Control Limit (UCL) - (1) Control limit for points above the central line in a control chart. (2) A line on a control chart used as a basis for judging whether variation from the data on the chart is due to special or common causes. Any point beyond the upper control limit is an indication of a special cause occurring. This limit is calculated from data collected on the system, it is not a specification or limit set by customers or management. Its symbol is UCL.

Upper Specification Limit (USL) - The upper limit of a specification. This limit is set as an aim for a system or process, it is usually set by the customer of the process, engineering, or management. The symbol for the upper specification is USL–upper specification limit.

Upstream
- If the process by which something is accomplished or produced is thought of as a "flow" from one stage of the process to another, then "upstream" refers to the stages of the process that come before the stage that serves as the reference point. Improvements or innovations made upstream in a process (e.g., Design of product or process) often can have high-leverage impact on results downstream.

Uptime -
See “equipment availability.”

User Group
- A voluntary and often informal association of individuals or organizations that are "using" a particular method, or theory and wish to share information, discuss common issues and/or pool resources to accomplish their respective goals. Aptly described as "a safe place to discuss ideas and problems". [Origin: users of specific computer hardware and/or software].

User-based
- A definition of service or product quality that is customer centered.