17.2. RSS TOLERANCE CALCULATIONS

Now, let's use the RSS (root sum-of-squares) approach to calculating tolerances. What should be the tolerance on each part if we assume that ±3 sigma (99.73%) of the products are within tolerance?

Assume ±3 Sigma of Products Are Within Specification

Unless you have specific data showing otherwise, assume that ±3 sigma (99.73%) of the products are within tolerance. This is a general rule of thumb, since few products are made totally within specification.

Assume that in this example we want ±3 sigma of the total stack height to be within the 10" ± 0.100" tolerance specification, the same as assumed with the traditional ...

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