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Usually when we compute CPK, we also use X Bar-R Control Chart. We use these formulas: CPK=Min(CPU, CPL) , CPU=(USL-X Bar)/(3*Sigma hat) , CPL=(X Bar-LSL)/(3*Sigma hat) , Sigma hat=R Bar/d2
My boss wants to use X Bar-S Control Chart. This creates a problem-the R Bar is no long available. How am I going to compute CPK?
I’m thinking of using the formula Sigma hat=S Bar/c4 . My concern is-is this acceptable?
My boss wants to use X Bar-S Control Chart. This creates a problem-the R Bar is no long available. How am I going to compute CPK?
I’m thinking of using the formula Sigma hat=S Bar/c4 . My concern is-is this acceptable?