X̄- and R-Chart Control Limits Based on a Small Number of Subgroups
- 1 January 1969
- journal article
- research article
- Published by Taylor & Francis in Journal of Quality Technology
- Vol. 1 (1) , 17-26
- https://doi.org/10.1080/00224065.1969.11980343
Abstract
A common rule of thumb is that conventional control limits for X̄ and R charts, no standards given, should be based on at least 25 subgroups. This article presents information for evaluating the lack of reliability of these control limits when they are based on a smaller number of subgroups. Then, another method is presented for setting the control limits for these charts so that they can be reliably used regardless of how few subgroups have been inspected.Keywords
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