Electronic body fat scales have become very high-tech devices. From bathroom scales with Wi-Fi connectivity to ultra-precise devices for research or industry, modern scales provide very accurate measurements almost instantly. However, this was not always the case and today we take a look at the different systems that have emerged over the millennia.

The birth of the scale was a necessity. As trade developed in ancient times, merchants needed a way to assess the value of commodities that could not be calculated simply in fragments, such as irregularly shaped gold nuggets. The oldest remains of a scale have been found in the Indus Valley near present-day Pakistan, dating to a central pole around 2000 BC. Measurements are made by placing the object being measured on one plate and the weighted gemstones on the other plate until equilibrium is reached.

It wasn't until the industrial age that scales knew of any major technological improvements. It was not until the late 18th century that new methods of measuring mass that did not rely on counterweights began to appear. The spring balance was invented around 1770 by English balance maker Richard Salter. A spring balance, as the name suggests, measures the pressure (or tension) exerted on a spring to infer the weight of an object. Spring scales are still fairly common today because they are so cheap to manufacture, but they are not as accurate as the electronic systems designed and perfected in the 20th century.

Most modern scales rely on electronic devices to measure the user's weight. By sticking resistors on deformable materials and energizing them through them, it is possible to detect the change in electrical conductivity of the resistors in relation to the amount of pressure exerted on the material, thereby inferring the weight of a person (or object) standing on the scale. The highest-end scales also act as impedance meters, capable of calculating the ratio of body fat to lean muscle mass. Impedance measurements are made by generating a very small current across the surface of the scale and measuring the resistance the current encounters as it travels through the body. Lean body mass is a better conductor than fat mass, so the ratio of the two in the body can be deduced.

Xiangshan Zhengtai Electrical Appliance Co., Ltd. is a digital scale supplier from China. The company designs, processes and sells digital luggage scales, Bluetooth Scale, and other electronic scale products.