What is the optimum regime for calibration bias adjustments?

Abstract

Fonterra, a New Zealand Dairy Company, processes milk into various products, including milk powder and cheese, for export all around the world. The challenge for Fonterra is to guarantee that the composition of a product meets agreed contract specifications. The Study Group was asked to determine if the calibration monitoring scheme currently in place at Fonterra could be improved and what other information could be derived from monitoring. As a result of the Study Group's deliberations, a number of recommendations have been made---one of which has already been implemented (scanning a check-cell daily to monitor the instruments' performance). Fonterra are currently investigating the impact of some of the other recommendations made by the group, including switching to using mean values from median values, and implementing a strategy to monitor laboratory reference values.