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CWI Medical

Weighing Scales 101

by Noah Lam, Chief Operating Officer of CWI Medical


You step on a scale, the dial points to a number, you slide a little weight on a balance or a digital display reveals your weight. Then you step off and decide what to do next, but have you ever wondered how these scales work?

As Archimedes once said “Give me a place to stand and I will move the Earth.” This is the premise behind a scale. The original scales used a beam that sits on a pivot point which becomes a fulcrum. This type of scale is also known as a center beam scale. A combination of reference weights would be hung on one side of the beam and on the other end would be the object to be weighed. When the beam is level, you would count the reference weight to determine the results.
Similar to the center beam scales, the upright beam scale you see in your doctor’s office is an off-center scale. These scales can use smaller reference weights because the fulcrum position of the beam is in relation to the weights and the force imposed on the plate. These scales are known as physician scales or a balance beam.

At home, most usually have a mechanical dial scale, which uses levers connected to a plate with a spring. As a weight is placed on the plate, a spring stretches and a pivot point translates the up and down force to a side motion. This side motion is used to create the rotational motion that you see on the dial of the scale. These type of scales are typically found in bathrooms.

Today, digital scales are becoming more prominent. Digital scales use load cell technology that incorporates electro-mechanical transducers that translate the weight into an electrical voltage. The difference in voltage can be measured and the results are shown on an LED or LCD display. Most digital scales use batteries, while others need to be plugged in. Some models include a calculator to measure your Body Mass Index or probes to measure body fat percentage.

Body Mass Index is the measurement of body fat based on height and weight. A body mass index of less than 18.5 is considered to be underweight, 18.5 to 24.9 is considered normal, 25 to 29.9 is overweight, and over 30 is obese. To calculate your Body Mass Index, multiply 703 with your weight in pounds then divide by your height in inches and divide again by your height.

All scales have a weight capacity, some are as small as a kitchen scale measuring grams to scales big enough to measure a truck. Exceeding the capacity of a scale will damage it.

Detecto and Health-o-meter both have been leaders in the healthcare industries with the ever popular physician scales that we always see in the doctor’s office. Infant scales are designed to measure small babies. Chair scales are for those who can not stand. Wheelchair scales are unique since they need to accommodate the wheelchair. Some use ramps for each side of the wheels, and other types use a platform to measure weight.


Noah Lam has over 15 years of experience of providing high quality medical supplies and healthcare products from Acute Care Facilities to parents and children. His company, CWI Medical is a leading provider of clinical diabetic nutrition to healthcare facilities, dialysis centers, and for home use. In addition, CWI Medical is an ACHC Accredited organization maintaining standards of excellence in the Healthcare Field. For more information, please visit

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