There are other out-of-control rules that are sometimes used with x¯ charts. One is “15 points in a row within the 1σ level.” That is, 15 consecutive points fall between μ−σ/n and μ+σ/n. This signal suggests either that the value of σ used for the chart is too large or that careless measurement is producing results that are suspiciously close to the target. Find the probability that the next 15 points will give this signal when the process remains in control with the given μ and σ