The body tester in the gym. In fact, the principle of the body tester is no different from that of the body fat scale. With two more handle electrodes, the accuracy will not be improved too much. Mainly, the body tester has the function of outputting "analysis report", which contains not only basic data such as body fat rate, but also various analytical, evaluative and suggestive data, such as basal metabolic rate, visceral fat, segmental muscle, various evaluation scores and so on.
These further data are calculated by applying the formula again according to the measured basic data (such as body composition). As mentioned above, there is already a big error in the data of body composition, and the formula itself does not necessarily match the measured person, so the result obtained by further applying the formula is bound to have a big error.
The body fat scale or body fat measuring instrument on the market is "scientific in principle and mature in technology, but the data error is large, which is for reference only"
Both the body fat scale and the body measuring instrument measure the body composition through bioelectrical impedance analysis (BIA). Simply put, fat, muscle, bone and other tissues are distinguished by different electrical conductivity. After measuring the resistance value, the proportion of body components, such as body fat percentage, is calculated by formula.
In fact, BIA method is a quite mature technology, which is widely used in medical field and various physiological laboratories, but it requires very harsh test conditions to get accurate values.
For example, we need enough electrode pads, well-designed contact position with skin, suitable temperature and humidity in the test environment, formulas and various coefficients adjusted according to different situations, and even have clear requirements for the recent exercise, diet and posture of the subjects. The body fat scale we use every day, although backed by scientific principles and mature technology, is far from meeting the accuracy requirements in operation.