What type of control chart you are talking about? Xbar-R...
If it is Xbar-R chart, there are two ways of estimate the sigma. One is by Rbar (Rbar/d2), the other is by Sbar (Sbar/C4). There will be a small difference. But what the hell, if the difference is small, for engineer, it is not important as long as you stick to the same way of calculation.:lol:
2003-01-23 19:28