Repeatability
Repeatability turns up in 2 fields: statistics, metrology. Here is what it means to the people in each one.
Repeatability in statistics
Scatter in the readings when one person and one gauge measure the same part over and over with nothing else changed.
Repeatability is the short-term, within-system spread of a measurement, often called equipment variation (EV). It captures gauge noise, fixturing play and small positioning differences, estimated from repeated readings of one part with nothing else changed. Poor repeatability points at the instrument itself: worn contacts, vibration, electrical noise, unstable focus or a part that does not seat the same way twice.
"Repeatability is fine, the tool reads within 0.2 nm on back-to-back loads. The problem is between the two tools."
Repeatability in metrology
How tightly readings bunch when one person repeats a measurement with the same setup, in one place, in one short sitting.
The scatter that shows up when one person repeats the same measurement on the same item, with the same setup and in the same place, within one short session. It is expressed as the standard deviation of those replicates and enters most budgets as a Type A component. Repeatability is the smallest scatter a method will ever show, since it leaves out day-to-day and person-to-person effects.
"Repeatability on the bore gauge is 0.4 microns over ten readings, so scatter isn't the problem."