MRC:
A feature of the item of supply which must be specifically recorded when the reference number covers a range of items.ZZZY
Reference Number Differentiating Characteristics:
An item that supports subsafe critical systems and requires objective quality evidence that quality assurance requirement have been met, including cetification of tests for hydrostatic and / or operational testing and item serialization traceable to the certifications during initial procurement and anysubsequent repairs. Government source inspection is involved