All variation associated with a measurement process. Potential sources of variation include gages, standards, procedures, software, environmental components, as well as others.
When measuring the output from a process, consider both the part-to-part variation as well as the measurement system variation. For example, you have a known standard that is exactly 5.00g. You weigh it multiple times and get the following readings: 5.01g, 4.99g, 4.97g, 5.03g, 5.01g. The differences in the measurements are due to measurement system variation. If, however, you weigh different parts that come off your manufacturing line, are the differences due to measurement system variation or due to actual differences in the parts themselves? Use Minitab's measurement system analysis tools to determine the sources of variation. If the measurement system variation is large compared to part-to-part variation, the measurements may not provide useful information.
Like any other process, a measurement system is subject to both common and special cause variation. To control the measurement system variation, you must first identify the sources of the variation, then you must either eliminate or reduce the various causes.