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Article Summary: "People figured out that they needed standards of weight and measure, as they are called, in the earliest of civilizations so that everyone would understand what they were getting when they bought something. All around the world you see hanging scales in the markets to weigh produce and other foods. Even in the age of automated food weighing at the check-out counter, you still see hanging scales in the grocery store."

# Why Do We Have Units of Measurement?

 When you go to the grocery store to buy cereal, for example, there's a tag on the shelf that tells you the price per ounce of cereal so you can compare the cost of one brand over another. Without a standard measure of weight, in this case an ounce, you wouldn't know exactly what you are paying for. People figured out that they needed standards of weight and measure, as they are called, in the earliest of civilizations so that everyone would understand what they were getting when they bought something. All around the world you see hanging scales in the markets to weigh produce and other foods. Even in the age of automated food weighing at the check-out counter, you still see hanging scales in the grocery store. Precious metals like gold and silver are sold by the ounce as well except they are sold by the troy ounce. The weight of a troy ounce was set up in the 12th century to be the weight of one grain of barley! So a troy ounce has a different weight than the ordinary ounce that we use to measure grocery items. Can you see why it is important to understand what each unit of measure means? You get an entirely different amount of product if you buy a regular ounce versus a troy ounce. But, of course, you only deal with troy ounces when you are buying precious metals. Let's name some other units of measurement like those that apply to distance. For example, there are inches, feet, yards and miles, right? But wait - what about centimeters, meters and kilometers? Don't these units measure distance too? It's important to know that there are different measuring systems. The American system of measuring distance in inches, feet and yards is based upon the units from England because the earliest American colonists came from there. But much of the rest of the world uses the metric system of centimeters, meters and kilometers. While 1 foot is the same as 12 inches and a yard is 36 inches, the metric system uses multiples of 10. In metric 1 meter is 100 centimeters and a kilometer is 1000 meters. With all the international business that occurs today, it's important to be able to work with metric units of measurement. In fact, in the 1980's the federal government tried to introduce metric in the United States. Speedometers on the cars from that time showed both miles per hour and kilometers per hour. You still might be able to find some interstate highway signs showing distances in both miles and kilometers. But these attempts at changing to metric failed as you well know. This failure should give you some idea at how important standard units of measurement are to people. Once a standard is set, it is very difficult to change it. Science is another area where units of measurement are critical. There are lots of measurements in chemistry and physics that you will learn about. But a unit of measure that you might already be familiar with is a watt of electricity. When you purchase an everyday light bulb it is typically labeled as 40, 60 or 100 watts. This standardized number tells you the amount of electricity that the bulb uses and how bright the light will be. Looking at watts a little further, the electric bill for your house is based upon how many kilowatts of electricity you've used for the month. If a kilometer is 1000 meters, how many watts are in a kilowatt? In measurement terms, kilo means 1000. Measurements are all around us every day to provide standards and stability to everyday life.