Defining the limits of accuracy for all measuring instruments. The limits of measurement must be better than the required limits for the product, process and safety. If the measuring instrument fails to meet calibration limits then the product, process or safety could have been compromised. If a factor of two is set, and if the measuring instrument fails calibration there is a margin allowed before any quality issues are raised. The factor should be as large as possible, the larger the factor the greater the safety margin. The setting of the factor often depends upon the repeatability of reading.
