Repeatability

Repeatability or test-retest reliability is the variation in measurements taken by a single person or instrument on the same item and under the same conditions. A measurement may be said to be repeatable when this variation is smaller than some agreed limit. According to the Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results, repeatability conditions include:

Repeatability methods were developed by Bland and Altman (1986). The repeatability coefficient is a precision measure which represents the value below which the absolute difference between two repeated test results may be expected to lie with a probability of 95%. The standard deviation under repeatability conditions is part of precision and accuracy.
 * the same measurement procedure
 * the same observer
 * the same measuring instrument, used under the same conditions
 * the same location
 * repetition over a short period of time.