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of parts from the average size is in the range from -3 to +3.
The calculation error makes 0.27% in total, which is completely
admissible. If the processing tolerance is greater than 6, then
all the preforms are suitable in size, and there is practically no
gap.

Random errors in the sizes of lots of parts, which are
processed practically, are subject to the law of normal
distribution. Equation of the normal distribution curve

2 2
Y  e  x /( 2 ) /( 2 ), (8.3)

where Y – probability density; e – the basis of the natural
logarithm (е =2,718...).
The shape of the curves of the normal distribution is
characterized by the mean square deviation and corresponds to
the value of the scattering (Fig. 9.3). The less , the smaller
dispersion of the sizes (the curve is extended upwards); at
larger  scattering sizes are larger (the curve has a stretched
shape).
The maximum ordinate of the normal curve corresponds
to the abscissa A ср:

Y max  1 /( 2 )  / 4 , 0 .  (8.4)

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