The traditional bathroom scale is used to measure a person's body weight. It is based on a spring system that uses the weight of the person to depress a lever, which in turn rotates a sprocket attached to the dial. The dial rotates until it stops, and a plastic marker marks the person's weight. A home-use bathroom scale has a margin of error of ±0.25 lb (±0.12 kg). Scales for bathrooms or kitchens are generally designed as spring balances.
Units of measurements have been used for all of antiquity. People have always used some type of set standard for trade. The first known measurement device was used by the Romans 2,000 years ago. They devised an equal beam scale which was shaped like the letter T with both arms measuring 7.4 in (18.8 cm) wide. Attached to each arm were metal pans that were typically 1.5 in (4 cm) in diameter.
The first known unit of weight was the wheat seed. The ancient Romans and Greeks used this standard to measure any other object against, generally for barter or trade. For instance, farmers would bring their crops to sell and they would be weighed against the known standard of wheat grain. X-amount of produce was equal to X-amount of grain needed to maintain the equilibrium of the balance. The Arabs improved on these techniques and established weight standards for gold, silver, and gems.
By the thirteenth century trade had become much more widespread, but people in different parts of the world (or even within the same country) used different standards of measurement. King Edward I of England established a base standard of measurement to which objects or materials could be compared to. This standard soon traveled through trade and became somewhat acceptable in other parts of the world.
In 1793, the French government devised a system based on a line running along the ground through Paris that measured the distance from the North Pole to the Equator. The French called this the metric system. People were unfamiliar with this system and it was not fully enforced until 1837 when it became the standard in European countries.
Scales themselves continued to evolve to meet both the distributor and customer's needs. Customer's wanted to be able to count on the accuracy of the distributor's scales to make sure that they were not being cheated. The first scales used a simple balance beam to weigh an object against a known standard.
The first spring balance was brought into widespread use in the eighteenth century. In Bilston, England Richard Salter began making what is today known as a fisherman's scale which used a spring balance to measure weight. The Salter brand was also the first company in England to marked bathroom scales. Modern home scales have evolved from these early industrial prototypes. Today, the scale is based on the same spring balance idea.
The case of the spring scale is manufactured from stainless steel or aluminum. The interior is composed of metal springs, pins, gears, and plastic. The gears can be made from aluminum, copper, brass, bronze, stainless, steel, nickel silver, monel, zinc, iron, or plastic. The non-slip mat is formed from a mix of poly vinyl chloride and rubber.
There are many different types of scales; solar, electronic, digital, and spring to name a few. The scales may also differ on what they measure. Some scales are able to measure a person's body fat ratio. The color and size of scales vary greatly to meet all customer needs.
A typical spring scale is comprised of weight transmitting levers, a weight sensing mechanism, and dial enclosed in a metal casing. Generally, the scale is equipped with a non-slip pad on the platform so that the person does not slip and fall off the scale.
The parts used to manufacture the scale are checked for defects. Any defective parts that can be salvaged are removed and reused. Parts that are extremely damaged are discarded or recycled. The workers check the calibration of the scale against a known weight before it is packaged. Typically the scale should be able to detect weight within 0.25 lb (0.12 kg).
Any excess or defective parts are assessed for quality and then either reused or discarded.
As technology advances, so does the accuracy and application of scales. Today scales can measure not just weight but also body fat. These scales send a mild electrical current through the person's feet and up the rest of the body. The more quickly the signal travels through the body, the less fat. Software is also being developed that allows the scale to keep track of a person's weight loss or gain. Some are even able to track the weights of more than one person. These systems will be able to hook up to software on the home computer to better track weight loss or gain.
Salter Scales Online. December 2001.< http://www.salterhousewares.com >.
Deirdre S. Blanchfield