不论是托盘天平还是物理天平，在测量物体质量前都要调节横梁平衡，那么横梁不平衡时，怎样调节横梁上的平衡螺母，才能使指针指在分度盘的中线处呢？从天平的结构上看，指针固定在横梁上且与横梁垂直，如果横梁不在水平位置，指针就不会指在分度盘的中线处，请看下图．图甲中 Regardless of whether it is a tray balance or a physical balance, the balance of the beam must be adjusted before measuring the mass of the object. Then, when the beam is unbalanced, how can the balance nut on the beam be adjusted so that the pointer points to the center line of the index plate? From the perspective of the structure of the balance, the pointer is fixed on the beam and perpendicular to the beam. If the beam is not in the horizontal position, the pointer will not refer to the center of the index plate. See the figure below. Figure A