The problem of production variability in serial manufacturing lines with un
reliable machines is addressed. Bernoulli statistics of machine reliability
are assumed. Three problems are considered: the problem of production vari
ance, the problem of constant demand satisfaction, and the problem of rando
m demand satisfaction generated by another (unreliable) production line. Fo
r all three problems, bounds on the respective variability measures are der
ived. These bounds show that long lines smooth out the production and reduc
e the variability. More precisely, these bounds state that the production v
ariability of a line with many machines is smaller than that of a single ma
chine system with production volume and reliability characteristics similar
to those of the longer line. Since all the variability measures for a sing
le machine line can be calculated relatively easily, these bounds provide a
nalytical tools for analysis and design of serial production lines from the
point of view of the customer demand satisfaction.