Seven points to note when using a balance as a measuring instrument

   The balance is a more precise measuring tool, and its structure is complex, and its use is cumbersome and difficult to master. Grasping the following precautions will help you understand and master it.
　　1. Check carefully: Observe the nameplate of the balance, and clarify the weighing capacity of the balance (that is, the maximum mass that can be weighed at one time) and the sensitivity (that is, the graduation value on the scale where the cursor is located). The mass of the object measured cannot exceed the weighing capacity of the balance.
　　2. How to place: Place the balance on a horizontal platform and place the cursor at the zero scale line on the left end of the scale (mis-pointing warning: this step is easy to ignore).
　　3. Adjust the nut: Adjust the balance nuts at both ends of the balance beam (some balances have only one) to balance the beam. The sign of a balanced beam is: the pointer points to the center of the scale plate. If the pointer swings equally at the left and right ends, it also indicates that the beam is balanced.
　　Tips: Many students do not know which direction to adjust the balance nut to balance the beam. You can think of a seesaw. If the left end of the seesaw is higher than the right end, what should we do? Yes, we can let the person on the left end move to the left, or we can let the person on the right end move to the left, that is, the higher end moves to the side. The moving direction of the balance nut is similar to the moving direction of the person, so simply remember "the nut moves toward the higher place".
　　4. Weighing: Put the object to be measured in the left pan, use tweezers (note: not with your hands) to add or subtract weights to the right pan (simply remember "left object, right weight") and adjust the position of the cursor on the scale until the beam is balanced.
　　Tips: The method of adding weights is to add them in order from large to small mass. When a larger weight is placed on the right pan, the right end of the beam sinks, and a smaller weight should be replaced, and so on. When should we start moving the cursor? You should know that moving the cursor to the right is equivalent to adding weights to the right pan, and the reading when the cursor moves to the rightmost end is equal to the smallest weight value. Therefore, when the smallest weight is placed on the right pan, the right end of the beam sinks. At this time, the smallest weight should be taken down and the cursor should be moved to the right.
　　Mistake warning: From the above operation process, we can understand that the "flatness" of the balance is reflected in three places: first, the base should be placed horizontally; second, the crossbeam should be horizontal before weighing, which requires adjusting the balance nut; third, the crossbeam should be horizontal during weighing, and the balance nut must not be adjusted at this time. What is needed is to add or subtract weights and move the cursor. Although the latter two times require the crossbeam to be horizontal, the methods adopted are different.
　　5. Record: The mass of the object being measured = the total mass of the weights in the pan + the scale value corresponding to the cursor on the ruler
　　Mistake warning: Regarding the cursor reading, many students are confused about whether to read the scale value corresponding to the left end of the cursor on the ruler or the right end. To answer this question, you can think about it first: before weighing, we need to put the cursor at the zero scale line on the left end of the ruler. So, is it the left end or the right end of the cursor aligned with the zero scale line? Of course it is the left end. So when reading the cursor, you can only read the left end.
　　6. Taboos: Keep the balance dry and clean. Therefore, the mass of liquid cannot be measured directly, and a container must be used. Powdered solids cannot be measured directly either, and the same paper can be placed on each of the left and right plates.
　　7. Measurement methods under special circumstances:
　　The mass is less than the scale value of the scale: measure more and count less (such as measuring the mass of a pin).
　　The mass is greater than the range of the scale: measure less and count more (such as measuring the mass of a large stone, you can measure the mass of the same small stone, and then use the volume ratio to find it).
　　Measuring the mass of liquid: Be accurate and scientific. For example, to measure how much water can be contained in an ink bottle, you must do the following: ① Fill the ink bottle with water, and use a balance to measure the total mass of the ink bottle and water; ② Use a balance to measure the mass of the empty ink bottle; ③ Calculate the mass of the water. However, there are two possible operation sequences: ①②③ or ②①③. Both methods can measure the quality of water. However, if you use the former method, you must pour out the water in the ink bottle. However, the water in the ink bottle cannot be poured out completely. There will be some water on the bottle wall, which will result in inaccurate measurement. Therefore, to measure accurately and scientifically, you must use the second method.