The inertial system of fighting vehicle existed bracket error due to its two-axis gyro platform structure, and this could influence the heading precision.

Methods of spherical trigonometry and direction cosine matrix were applied respectively to derive the bracket error, and the two methods had the same error formula and the same calculation results.

If the empty bracket pair is omitted, it is an error, but an error that the compiler is unlikely to catch; the program may fail at run time.