Every process has variations, and measurement is a process. Variations can be systematic or random. In Six Sigma , Measurement System Analysis (MSA) is used to evaluate measurement results.

The term MSA comes from AIAG (Automotive Industry Action Group). The MSA guidelines describe various methods to assess different aspects of measurement system capability:

▪ MSA Type 1 – Determination of bias (accuracy) and repeatability (precision)
▪ MSA Type 2 – Determination of repeatability and reproducibility
▪ MSA Type 3 – Similar to Type 2 but without operator influence (automated measurement systems)
▪ MSA Type 4 – Determination of the measurement system’s linearity
▪ MSA Type 5 – Determination of the measurement system’s stability
▪ MSA Type 6 – For gauge testing
▪ MSA Type 7 – Related to ISO 22514-7 (Bowker Test)