Mechanical scales use cross-arranged levers to support your weight and distribute it evenly across the scale. Your weight then presses on these levers, which push the center spring down. The spring uses a slightly more complicated mechanism to turn the dial with the weight on it.

There are many different ways this can cause problems. For one thing, to be small enough to fit in the bathroom, scales like this use a special mathematical ratio between the point where your weight rests on the lever and the lever's fulcrum. This effectively reduces your weight by a factor, usually 10 or 12. The reason is space; the springs acting as resistance and the pull to turn the dial don't need to be as strong. Without the scale, you see a larger scale.

The problem here is that losing weight through ratios means small fluctuations may be missed. There is some error in the display as it is just a physical radial dial. If the springs are not as strong as they should be, or if the lever position is slightly off from true, or if the scale is old and worn out, it may now display your weight correctly.

As with any mechanical device, proper calibration is critical for accurate readings. That's why industrial scales have tight tolerances, their manufacturing process is scrutinized, and extensive testing is done to ensure their accuracy.

Xiangshan Zhengtai Electrical Appliance Co., Ltd. is a digital scale supplier from China. The electronic scale factory designs, processes and sells personal care scales, digital pocket scales, and other electronic scale products.