the entire flight. Assignments are made by the ARTCC computer on the basis of the National Beacon Code Allocation Plan. The equipment is also designed to receive Mode C altitude information from the aircraft. NOTE- Refer to figures with explanatory legends for an illustration of the target symbology depicted on radar scopes in the NAS Stage A (en route), the ARTS III (terminal) Systems, and other nonautomated (broadband) radar systems. (See FIG 4-5-3 and FIG 4-5-4.) d. It should be emphasized that aircraft transponders greatly improve the effectiveness of radar systems. REFERENCE- AIM, Para 4-1-20, Transponder and ADS-B Out Operation. 4-5-4 Surveillance Systems