
The Average is 20 millimeters, but individually they vary from 19.10mm to 20.90mm. This is OK with our customers because their specification calls for and Average of 20mm with a Tolerance of +/1.5mm. That means they will accept anything between 18.5 and
Our problem is to keep the widget cutting machines at the center of 20.0mm and to not let individuals vary (disperse) more than they did in this lot.
All of the gadgets we measured were made at one time (the same Run) on the same machine by the same operator and from the same material lot. Because of all these things being the same, we can be quite sure that the Pattern of their Variation will almost e
We would also know that the greatest Individual Variations will be quite close to +/3 s. This is a Spread of 6 Standard Deviations.
The difference between the Longest (20.9mm) and the Shortest (19.1mm) is 1.80mm. One sixth of 1.80 is 0.3. So…. The standard deviation is 0.3mm.
Since we measured every widget, we measured the entire Population. We can do the same thing with a Sample.
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