Specifications don't always tell the whole story

When choosing a motion-control product for a particular application, products are commonly chosen based on the specifications supplied by the manufacturer. These specifications, however, are often gathered under ideal conditions and rarely replicate an actual real-life environment. Hence, the specifications may not be an accurate indication of how the device performs outside the test laboratory. Moreover, a wide range of values can be obtained for a given specification in the same test setup, depending on the methodology and mathematics used. So how the equipment specification is obtained-from environmental factors to methodology-is actually as important as the number itself. To demonstrate that a wide variety of "specifications" can be generated for a single characteristic we compare the measurement of one parameter-repeatability-with one test setup but with the data gathered in a variety of ways. Differences include the number of data points, the "randomness" of those points, different statistical and mathe- matical methods, and which metrology standard is used.