Since he cannot make the supplier accountable for his own measuring uncertainty, the customer can only file claims if these extended limits are violated. This is especially likely to lead to a contradiction if the customer’s own measuring uncertainty is excessively high. The customer must instruct his own quality assurance department to refrain from using any parts for which a certain tolerance deviation has been measured. This applies especially in cases where the measuring machine used in the incoming inspection department has a measuring uncertainty equal to or lower than the one used by the supplier. To prevent this from happening, the customer should prescribe a closer tolerance to the supplier [7]. The term “contractual tolerance” can be used to describe this situation. The following tolerance chain results:

Contractual tolerance = specified tolerance

                                      – measuring uncertainty of customer

Process tolerance      = contractual tolerance

                                       – measuring uncertainty of supplier

Under these conditions, it can be ensured that the terms of the contract are clearly defined and verifiable. One example of this case is shown in Figure 56. Here, the tolerance for the supplier has been reduced to the contractual tolerance. This means that the customer can accept all parts approved by the supplier as within tolerance without having to make any concessions with respect to quality assurance. Since this procedure could result in higher costs, it creates a demand for sufficiently accurate coordinate measuring technology both in the supplier’s and in the customer’s inspection department.