There is a rotatable steel ring outside the military watch of China Army. What's the use?

The first is to look at the direction. When time is split in two, time is aimed at the sun, and the direction of 12 point is north. Then turn the bezel to a better position, the red star is aligned with 12, and all eight directions are clear.

The second is used for ranging, which uses the angle difference of distant markers to calculate the target distance.

The third is that the above two functions can be combined to locate.