Body fat scale is a weighing instrument that can measure fat, moisture and so on besides weight. At present, there are two kinds of sensors for measuring body fat on the market: ito film and electrode sheet. The principle of human body fat scale is that muscle contains more water such as blood and can conduct electricity, while fat is not. Because the channel conductor of current in the body is muscle, the weight of muscle can be known from the difficulty of current passing, so as to judge the proportion of muscle in the weight. It is found that when an electrical signal with a certain frequency passes through the human body, the "impedance value" of the fat part is higher than that of muscles and other tissues of the human body. When an electrical signal with a safe specific frequency passes through the human body, the electrical signal will change in different degrees due to the different "impedance values" of the human body. Principle: Muscle contains more water such as blood, which can conduct electricity, but fat can't. Because the channel conductor of current in the body is muscle, the weight of muscle can be known from the difficulty of current passing, so it can be judged that people with less muscle have a higher proportion of fat. Correct health concept: A healthy body lies in the balance of body fat. Too much fat accumulation is harmful to the body, leading to various diseases. Human fat is an important part of the human body, which has important functions and functions in the human body, such as providing energy, protecting internal organs, maintaining body temperature, assisting the absorption of water-soluble vitamins, and participating in human metabolic activities. However, too much fat will affect human health, leading to diabetes, cardiovascular and cerebrovascular diseases. In addition, obese patients often face various troubles such as fear of heat, influence on body shape and fatigue. Therefore, doctors and experts suggest keeping your body shape within a certain range. With the improvement of people's living standards, health problems are paid more and more attention, which also promotes the development of human body composition measurement science. At present, there are many methods to measure human body composition, especially human body fat, mainly including underwater weighing method, skinfold anthropometry, bioelectrical impedance analysis (BIA) and so on. In addition, there are dual-energy X-ray absorption (DEXA), computed tomography (CT) and magnetic resonance imaging (MRI), which have developed rapidly in recent years, but these methods require expensive equipment and professional training, and patients are vulnerable to radiation, so they are not suitable for home use. BIA method is convenient to use, accurate in measurement results and relatively low in price, which is favored by consumers. According to the theory of BIA (Bio-electrical Impact Analysis), BIA is a technology to design and estimate body composition according to different conduction characteristics of different body tissues. When a current with a frequency greater than 50kHz is applied to the body tissue, the current can pass through the extracellular fluid. But part of the current will be absorbed by the cell membrane (resistance, R); Part of the current slows down because the cell membrane is temporarily charged, which is the reaction. Impedance (z) is the sum of resistance and resistance, and usually resistance accounts for more than 90%. According to the above principle, the electronic fat scale measures the biological impedance by using the electrode pads on the scale surface to contact with the legs of users, and then based on the input user data and the measured human body resistance, we can accurately measure human body components, such as the percentage of human body fat, the percentage of human body water, the percentage of human body muscle and the weight of bones, by using the formulas obtained from a large number of experiments.