Repeatability

Repeatability refers to the closeness of agreement between successive measurements of the same quantity, taken under specified, identical conditions. In most contexts, this means the same instrument, the same operator, the same location, and a short time interval between measurements. Repeatability focuses on the precision of the measurement process itself rather than external changes.

The concept is distinguished from reproducibility, which concerns variation when measurements are made under changed conditions such as different operators, different instruments, or different locations. In metrology and measurement system analysis, repeatability is one component of the overall measurement variation, with other components including bias (systematic error) and reproducibility.

Assessing repeatability typically involves taking multiple measurements of a single part or standard under the same setup and computing the spread of the results, such as the standard deviation or range. Statistical methods like ANOVA can separate repeatability from other sources of variation, and gauges such as Gage R&R studies express repeatability as part of the measurement system's precision.

Factors that influence repeatability include instrument precision, sensor drift, operator technique, fixture or setup consistency, sample heterogeneity, and environmental conditions such as temperature. Poor repeatability indicates higher measurement noise and can obscure true differences in the parts or quantities being measured.

Relation to accuracy: repeatability is a measure of precision—how close repeated measurements are to each other—rather than how close they are to the true value. Both high repeatability and low bias are desirable for reliable measurements.