Q.How many causes of variation will affect the quality of a product ?

Statistical Quality Control (SQC) monitors a manufacturing process while it runs, rather than only inspecting output afterward, by distinguishing chance (random) causes of variation — the many small, unavoidable influences that produce natural, stable variation and mean a process is 'in control' — from assignable causes, large identifiable factors (a worn tool, bad material, an untrained operator) that push a process 'out of control' and must be traced and co …