What is a reject and how does it relate to metrology and cost? A reject is any product that is faulty or not usable therefore must be discarded. Any reject that is built has been a waste of resources and so leads to increased costs for no reason. Using metrology throughout the production process will help to reduce the number of rejects that are accidentally made. With higher levels of precision and accuracy from the beginning, the science of measurement protects against the risk of rejects and therefore against the associated costs. Rejects will occur no matter what you do, whether because of operator error, material fault, or machine maintenance. However, by introducing metrology methods throughout, the number of rejects that result and the cost of having them are bound to decrease.