The CEC is a one-character numeric code that indicates whether or not an end item is essential to the operational readiness of a weapon system or the conduct of a military mission; or that an end item is a functional part contributing to the tactical and essential operations of an end item component or assembly whose failure would render the end item inoperable or incapable of fulfilling its mission; or that a repair or secondary depot reparable component is required for the safety and health of personnel, or is required by state or local laws.

A comparison of the code for a NSN is made for each higher order equipment application within the Marine Corps supply system. The code actually recorded is the most critical numeric derived from the comparison.