This thing is called annotation in AD (you must have used the Chinese version, this professional software, I feel it is better to use the English version, because many Chinese translations are not accurate, some translations are even wrong), and the bit number is more direct in China, not only the operational amplifier, but also the common bit number of all integrated circuits is U, which is the first letter of Unit. Remember the CPU, is the last U, Chinese means unit, device. The one after U? Is a wildcard, such as after the circuit drawing, automatically add the serial number,? It will be replaced by a numeric serial number, such as U1, U2, U3, representing the first integrated circuit, and the second integrated circuit.... The same class of components, in the same drawing, the digital serial number is not conflicting, for example, there is only one U1 in the whole drawing (after A, B, in fact, is the same type of U1 unit, such as double op amp has two op amp units, can be written as U1A, U1B, in fact, on the same chip) and usually in the circuit that indicates the resistance of R1, R2, R3 is the same thing, There are many similar bit numbers in the circuit, such as C1, C2, C3, inductor L1, L2, L3, diode D1, D2, D3, transistor\/field effect tube Q1, Q2, Q3 (also useful T, T1, T2, T3), etc., you see more pictures, draw some pictures, soon understand.