Capability of a characteristic with a uniform distribution. Suppose that a quality characteristic has the uniform distribution on 0 to 1. Figure shows the density curve. You can see that the process mean (the balance point of the density curve) is μ = 1/2. The standard deviation turns out to be σ = 0.289. Suppose also that LSL = 1/4 and USL = 3/4.
(a) Mark LSL and USL on a sketch of the density curve. What is Cpk? What percent of the output meets the specifications?
(b) For comparison, consider a process with Normally distributed output having mean μ = 1/2 and standard deviation σ = 0.289. This process has the same Cpk that you found in part (a). What percent of its output meets the specifications?
(c) What general fact do your calculations illustrate?