Measuring Tools

I saw a video clip for a high technology organization that described the importance of precision in measuring their parts. But the video showed a fellow using a dial indicator. It seems that a lot of people are not aware of the variability in this rather simple tool. If precision is really important, you don't use a tool that introduces 0.005" to 0.010" variability to the measurement process.

Measuring tools are used to assign a number to some feature of a part. In assigning this number, the tools vary. Sometimes a little and sometimes a lot. We can all appreciate the fact that if a lot of people measured the same part with the same measurement tool, there would be some disagreement in the responses. And if the same person measured the same part with the same measuring tool many times over, there would still be some disagreement. These are the sources of variation in the measuring process.

It is important, indeed necessary that the variability (repeatability and reproducibility) introduced by the measuring tool be known. Otherwise you make too many of the two types of errors - you accept product that should be rejected and you reject product that should be accepted.