In recent years the manufacturing industry has viewed the engineering design and development functions as being market-led. It follows, therefore, that the needs and demands of the customer must be fully considered at all stages of the design process. This means that the range of ‘customer usage’ should be taken into account throughout the design, development and testing processes.Software tools can be used as an aid in defining the ‘optimum’ testing profiles or procedures for any product under development matched closely to a customer profile. Such a system requires inputs from both ‘standard’ test sequences and customer measurements, which have to be manipulated to provide a suitable acceleration factor to reduce test and development time scales.This paper discusses the methods developed over many years in achieving the goals of testing based on customer usage. It deals with the methods used to map the customer environment, especially in determining the 90th percentile user. Finally, the procedures evolved to produce accurate accelerated testing procedures are elaborated.