Rulers are usually used to measure length or distance, while scales are used to measure the weight of objects. Whether it is a ruler or a balance, you need an accurate ruler or scale. Attention should be paid to precision and error when using to ensure the accuracy of measurement results. When using a ruler, it needs to be placed on a plane to ensure the accuracy of the measurement results. When using the level meter, it is necessary to put the object on the scale to keep it in balance, so as to accurately measure the weight of the object. Rulers and scales are commonly used teaching tools. In school mathematics courses, straightedge is widely used to measure the length and angle of line segments. In physics course, the balance is used to measure the mass of objects and is one of the important experimental tools. The ruler is a straight bar. You can easily measure the length by placing it next to the object to be measured. Balance is also very convenient. As long as you put an item on the balance, you can know its weight quickly. When using straightedge and level, we need to observe and measure carefully to get accurate results. A rigorous and serious attitude can also help us achieve better results in other areas.