Sampling is typically based on what criteria?

Sampling in the context of quality control and inspection is often based on the criterion of taking samples from a machinist over a period of time. This approach allows for a more comprehensive assessment of a machinist's work and the consistency of the manufacturing process. By collecting data from multiple samples over time, one can identify trends, variations, or issues that may arise, providing insights into the machining processes and the quality of the output.

Taking samples from a single piece of work does not offer a reliable indication of overall quality or trends, as it may not reflect the consistency of the machinist's performance or the variability of the manufacturing process. A random selection of parts can sometimes yield useful information, but it may not be as effective as monitoring a machinist over time, as it doesn’t necessarily account for specific skill levels or methods employed by a particular machinist. Averaging dimensions from multiple pieces could provide useful data, but without the context of the machinist's work over time, it may misrepresent the performance or quality trends. In summary, sampling over time gives a clearer picture of ongoing quality and adherence to standards in precision machining.