Why is the rod scale thick and thin?

"If the rod is as thick as the rod, in order to balance the weight of the rod, there is a fixed disk torque of the rod, and the weight of the rod is unnecessary ."
The answer upstairs makes sense to put the dingpan star in a proper position, but this answer is incorrect.

For smaller pole scales, the dingpan star is on the left side of the system (pivot point), that is, the rod side. In this way, the answer is correct.
However, if a large rod is called or there is no weighing rod scale, the Fixed Disk star is on the right side of the weighing system, that is, the side of the weighing disk. The Fixed Disk torque is in the same direction as the weighing plate gravity torque. This is a wrong answer.
Here, the left and right sides refer to those who hold the title.

There are two advantages of using a rod to make a thick and thin one.
First, reduce the weight of the rod. Due to the lever principle, the balance of weight symmetry far away from the system is more affected. In order to move the position of the Fixed Disk star to the left, it is most effective to put the main working scale of the indicator on the left side of the indicator system for easy operation. It is made of taper, which can facilitate sliding between the two sides.

Second, it meets the stress characteristics. The rod can be considered as a cantilever beam. The closer it is to the system, the larger the bending moment. The Rolling Rod is made into a thick and fine section, so that the section of the large bending moment is thick, and the section of the small bending moment is fine, in line with the force characteristics. In this way, the slider is light and beautiful, and the strength is sufficient.
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