Specifications
There are certain engineering documentation terms of military products which might not go in accordance with the American Identification languages. The section 3 of the standard clearly specifies those terms and helps product designers in offering a lucid definition about the items created for military.
It is mandatory for product designers to develop their products by adhering to the criteria set by the MIL-STD-130N standard. Merely setting the definition of product in accordance with the standard is not enough. The product designers have to take care of everything to satisfy the criteria. Item identification marking 'free text' often includes more information. A good designer retains all former part marking if an existing part, or typical part marking for a new part, then assigns a rectangular spot nearby for the UID, which is an additional label or small metal plate approximately where shown that contains the data matrix plus the 3 HRI that comprise the data matrix.
The requirement for the 3 HRI to be adjacent and unambiguous to the data matrix is a MIL-STD-130 requirement. There is no requirement it match the other part marking, for instance if the item were outsourced or is off-the-shelf, in which case the entity holding the Gov. contract may assign it their own part number and/or serial other than what exists on the product, and because they are labeling it will assign it their own cage code. A good example of this is a laptop used as an equipment controller; while it has a permissible ID on it, a company may wish to stick to cage-part-serial for ease of reporting and use their internal part number to report it because that's how they keep revision control for service purposes.
The most common designations for the adjacent HRI are MFR, PNO or P/N, and SER. MIL-STD-130N narrowed up the choices significantly, so drawings from pre-2008 may now show designations no longer preferred. Some companies simply use the designations 17V, 1P and S, which are surprising easy to adjust to.
Read more about this topic: MIL STD 130