ABSTRACT
At the top level, we can divide the sources of variation into two categories: instrumentation and process. Later on, we will refine the concept of process, but for now think of it as how the measuring device is used. This introduces elements of uncertainty that arise from the procedure and from the person executing it. For example, if I need to know the weight of a penny, the tool I would use is a balance, which has an inherent uncertainty associated with it. However, the balance is hardly the only thing that contributes to the variation in my data; much of that arises from how I use the balance. Similarly, if I need to measure the diameter of a penny, I can use a ruler or calipers, both of which can be traceable. As we discussed in Chapter 1, a certificate of traceability links our measurement to an accepted international standard. The certificate will also list the tolerance associated with the calipers or ruler, which is also a contributor to variation of measurement. This contribution is real, but it is often the smallest contributor to the overall variation that arises from the measurement process. We will illustrate this through two example measurement procedures-weighing a penny (where the measurand is weight) and determining the diameter of a penny (where the measurand is length).
