In clocks and watches, the rotation speed of the second hand is higher than that of the minute hand and the hour hand, so the rotation is most easily affected by external forces. On the other hand, when the wall clock scales from 12 to 6, the moment formed by the mass of the second hand on the second hand shaft is the same as the driving moment of the clock itself, which can help the second hand move forward. When the second hand starts from scale 6 to scale 12, the torque generated by the second hand itself is just opposite to the driving torque of the clock hand. The second hand reaches the maximum at scale 9, and once it exceeds this point, the torque decreases again. Therefore, when the driving energy of the clock is running out, and the torque of driving the second hand is getting weaker and weaker, and it can't resist the reverse torque of the second hand from scale 6 to scale 9, the second hand often stops at this position, especially near the 9 o'clock direction where the reverse torque is the largest.