
Statistical
Methods
Applied
to
Quality
Control
105
As one would imagine, it is virtually impossible to manufacture the same
article in large quantities and, at the same time, guarantee to tum out each
individual article exactly the same as the last one. There are many things
that can cause variations in the final product. Machinery can gradually, even
suddenly, go out of tolerance, operators may not be careful enough or the
material used may prove to be unsatisfactory.
Even if a manufacturer employs the most dedicated staff and has the best
quality-control systems, they are still liable to produce the odd component,
system or equipment that fails to meet