Quality is commonly thought of as degree of excellence and is a customer determination. It is the total composite product characteristics of marketing, engineering, manufacture and maintenance through which the product meets the expectations of the customer.

In the Total Quality Control System, control starts with the identification of customer requirements and ends only when the product is placed in the hands of a customer who is satisfied.

As the subject of quality control becomes more of a science and less of an art, in the sense that less reliance is placed on individual judgement and more on physical, chemical or microbiological tests treated statistically, certain principles should be recognised. Otherwise, the mechanical adherence to results obtained objectively may lead to gross errors which could be for greater than any incurred through human evaluation alone.