The air force plotter is not a technical arm, but an electronic countermeasure, which plays a vital role in missile launching and positioning. Cartographers of the China People's Liberation Army use specified symbols to mark information obtained by vision, radio or other means on battle maps. China's military service system is an important military system for citizens to join the army and other armed organizations, undertake military tasks or receive military training outside the army. It comes into being with the appearance of a country and changes with the country's economic situation, political system and military needs. China's military service system can be divided into two types: one is compulsory military service system, also known as conscription system. This system is that the state forces citizens to perform military service for a certain period of time within a certain age range through laws. The other is voluntary military service system, also known as conscription system. Under this system, citizens voluntarily enlist for military service and sign service contracts with the army.