A reference value is the known and correct measurement for each part. The reference value is used for comparison during measurement system analysis. For example, you have a reference part with known weight of 1 g that you use to calibrate your scales.
Related Journals of Reference Values and Decision Limits
Chemical Sciences Journal, Green and Sustainable Chemistry, Sustainable Chemistry and Pharmacy, Sustainable Chemical Processes, SusChem, ACS Sustainable Chemistry & Engineering, Green Chemistry