Question: how is usl and lsl calculated?
Answer: Upper Specification Limit (USL) and Lower Specification Limit (LSL). The Process Standard Deviation ( σ e s t ) (\sigma_{est}) (σest). This can be calculated directly from the individual data, or can be estimated by: σ e s t = R ˉ d 2 \sigma_{est} = \frac{\bar{R}}{d_2} σest=d2 Rˉ