[bluenose69]

The curve on your diagram makes me think that you've fitted a normal (Gaussian) curve to the data. By eye, the distribution looks a bit more like log-normal, and so if you're still working on the data, you might want to try that to see. Not that anything you've said or concluded seems wrong, though.

[andruby]

The normal curve in the image is there for operators to visually check if the machine results are normal distributed or not. It's a "stencil", not data.

The software actually does a Lilliefors normality test which returns a big No on this data.

[bluenose69]

Ah, thanks for the information.