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BS ISO 7870-1:2014 pdf free

BS ISO 7870-1:2014 pdf free.Control charts
Control charts are often used to judge the stability of a process. A process is considered to be in a “state of statistical control”(the process is effectively said to be “in statistical control”) if it is affected by random (or common or chance) causes only, i.e. if no extraordinary, unexpected, or special (or assignable) causes have entered the system. Such special causes can affect either the level at which the process is operating, the degree of variability around the process level, or both simultaneously.
Variations due to random or chance causes occur in a random fashion and are usually found to obey certain statistical laws. In essence, when a process is “in statistical control” it is possible to predict reliably the behaviour of that process, whereas when special (or assignable) causes enter the system,the process is subject to the results of these causes and the outcome cannot be predicted without information about their presence and effect. A process found not to be in a state of statistical control is said to be “out of control” and requires intervention to bring it into such a state. For certain economic or natural phenomena, there might be no known way to intervene and the control chart simply serves to identify a lack of control.
In addition to monitoring the stability of the process, control charts can also be used to judge the acceptability of a process. When the process is in statistical control, it is then possible to determine, with controlled risks of decision errors, if the process output does or does not meet product or service requirements. This is most effective when the variability of the process is small compared to the tolerance defined by the specifications. In such situations, the process level can temporarily shift to an out-of-control state, yet all product and service requirements are still being met. The control chart is then used to maintain the acceptable status of the process, notwithstanding the dynamic nature of the process level. Specific control charts, as described in ISO 7870-3, are needed in this case.BS ISO 7870-1 pdf download.

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