金鼓鈴旗之法
Regulations for Gongs, Drums, Bells, and Flags
金、鼓、鈴、旗，四者各有法。鼓之則進，重鼓則擊。金之則止，重金則退。鈴，傳令也。旗，麾之左則左，麾之右則右。奇兵則反是。
Gongs, drums, bells, and flags -- each of the four has its own regulations. A drumbeat signals advance; a double drumbeat signals attack. A gong signals halt; a double gong signals retreat. Bells transmit orders. When the flag waves left, go left; when it waves right, go right. For unorthodox troops, these signals are reversed.
Notes
The four signal instruments (金鼓鈴旗) formed the battlefield command-and-control system. 金 (jin) refers to bronze gongs or cymbals, not bells. The reversal of signals for 奇兵 (qi bing, 'unorthodox/flanking troops') is a security measure: if the enemy observes and decodes the main signal system, the flanking force still operates independently.