Same mean diff sigma, diff mean and same sigma...examples

Same mean different sigma

In a normal curve, most of the values tend to be crowded at the mean. Curves with the same mean and different standard deviation are as shown in the first diagram. (would upload the diagram later). Since the mean for all these curves coincides, the resultant figure looks like one curve mounting on top of the other.

The process representing curve with the steepest incline is the most capable because less values fall outside of the USL, LSL. So, the more sharper the nromal curve is, the better are the processes representing it.

Different mean, but same standard deviation

A good example of this is the heights of defense recruits in Russia, Japan, and India. Russian are the tallest, Indians the average, while the japanese are the shortest. When plotted, the curves (will upload the figure later) look like mountain ranges of same height. The curve representing the Japs will be to the extreme left, the Indians in middle, and the one represting the Russians to the extreme right.

* Note that in this example, the standard deviation in all the divisions would be the same.