How the garage/car example and the six-sigma (6σ) process are related?Amrendra Roy
Let the width of the garage (D) and that of the car (d) is measured in some units called as sigma or σ, further
Width of the garage is sacrosanct = 12σ (assume for the time being), then following three cases can occur depending on the ratio of D/d = Cp.
The process sigma level is 6σ when the Cp =2, this is represented by case ‘C’ given below. Point to be noted is that there is a margin of safety (=3σ) on both side of the car before car touches the garage. The ideal width of car is taken as 6σ (don’t ask why, right now!)
Process capability Cpk: is measured in the terms of the σ distance between the center of the of the car (C1) and the wall of the garage. Cpk tell us “how far is the car from left wall or the right wall of the garage (or customer’s specifications).
Hence, the are two Cpk vales,
Cpk is given by
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