Honest answer, I’ve heard both and they refer to same thing. It’s plus or minus 3 sigma or range of 6 sigma. They are equivalent.
That said it all depends on give and takes. How important is your process? How cheap is your engineer time? You can adjust the sigma amount as appropriate.
I use the rule of 3 sigma so I have a range of 6 standard deviations
Three sigma? What is this, astrology?? Six sigma or go home!
Then you earn an MBA and implement Lean Six Sigma.
Honest answer, I’ve heard both and they refer to same thing. It’s plus or minus 3 sigma or range of 6 sigma. They are equivalent.
That said it all depends on give and takes. How important is your process? How cheap is your engineer time? You can adjust the sigma amount as appropriate.