# BS ISO 7870-2:2013 pdf free

**BS ISO 7870-2**:2013 pdf free.Control charts-Shewhart control charts

The ISO/IEC Directives makes it necessary to depart from common SPC usage in respect to the differentiation between abbreviated terms and symbols. In ISO standards an abbreviated term and its symbol can differ in appearance in two ways: by font and by layout. To distinguish between abbreviated terms and symbols, abbreviated terms are given in Cambria upright and symbols in Cambria or Greek italics, as applicable.Whereas abbreviated terms can contain multiple letters, symbols consist only of a single letter. For example, the conventional abbreviation of upper control limit, UCL, is valid but its symbol in equations becomes UCL. The reason for this is to avoid misinterpretation of compound letters as an indication of multiplication.

A Shewhart control chart is a graph that is used to display a statistical measure obtained from either variables or attribute data. The control chart requires data from rational subgroups to be taken at approximately regular intervals from the process. The intervals may be defined in terms of time (for example hourly) or quantity (every lot). Usually, the data are obtained from the process in the form of samples or subgroups consisting of the same process characteristic, product or service with the same measurable units and the same subgroup size. From each subgroup, one or more subgroup characteristics are derived, such as the subgroup average, X , and the subgroup range, R, the standard deviation,s, or a countable characteristic such as the proportion of units with a given classification.

A Shewhart control chart is a plot of the values of a given subgroup characteristic versus the subgroup number. It consists of a centre line (CL) located at a reference value of the plotted characteristic. In establishing whether or not a state of statistical control exists, the reference value is usually the average

of the statistical measure being considered. For process control, the reference value may be the long-term value of the characteristic as stated in the product specifications; a value of the characteristic being plotted based on past experience with the process when in a state of statistical control, or based upon implied product or service target values. BS ISO 7870-2 pdf downlaod.