Hi, I find a difference when calculating the Sigma Level using the formula and when I input the values in the sigma calculator. Can someone explain this difference? The details are below. Process mean - 4.54, UCL- 5.11, LCL- 3.97 USL-4.63, LSL- 4.36, Std. dev- 0.19 Using formula, Z= USL- mean/ Std.dev, the sigmal level is 0.48 But, if I use the Sigma calculator, the sigma level comes out to 1.56....Why this difference?