My Reading on ASQ CQA HB Part V Part 1 small
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Charlie Ch<strong>on</strong>g/ Fi<strong>on</strong> Zhang<br />
<strong>Part</strong> VA<br />
Variable Data<br />
Variable data, also called c<strong>on</strong>tinuous data or measurement data, are collected from measurements of the items<br />
being evaluated. For example, the measurement of physical characteristics such as time, length, weight,<br />
pressure, or volume through inspecti<strong>on</strong>, testing, or measuring equipment c<strong>on</strong>stitutes variable data collecti<strong>on</strong>.<br />
Variable data can be measured and plotted <strong>on</strong> a c<strong>on</strong>tinuous scale and are often expressed as fracti<strong>on</strong>s or<br />
decimals.<br />
The X (average) chart and the R (range) chart are the most comm<strong>on</strong> types of c<strong>on</strong>trol charts for variable data.<br />
The X chart illustrates the average measurement of samples taken over time. The R chart illustrates the range<br />
of the measurements of the samples taken. For these charts to be accurate, it is critical that individual items<br />
composing the sample are pulled from the same basic producti<strong>on</strong> process. That is, the samples should be<br />
drawn around the same time, from the same machine, from the same raw material source, and so <strong>on</strong>.8 These<br />
charts are often used in c<strong>on</strong>juncti<strong>on</strong> with <strong>on</strong>e another to jointly record the mean and range of samples taken<br />
from the process at fairly regular intervals. Figure 18.10 shows an X and R chart.
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