Title: Metric and US Units of Measurement
Course: PW-Course-Import-Test > Section: Module 3: Acceptance Criteria

Module 3

A lot of the inspections that a quality inspector performs involve measuring components or parts to verify if they meet specifications. The drawing tells you the units of measurement, and it is very essential that the inspection is performed in those units. Here we will learn about the two units of measurements that are most common in the world today and how to differentiate between the two units of measurements.

Metric and US Units of Measurement

There are two systems of measurement that exist in the world today. The Metric System and the U.S. System. The U.S. system is also known as the Imperial System or the Standard Measurement System. The Imperial System was introduced in the United States in 1866, but the U.S. remains the only industrialized nation that has not adopted the Metric System. The only two other countries that use the Imperial System are Myanmar and Liberia.

The Metric System was introduced in 1799 by the First French Republic but over the years the definitions of the metre and the kilogram have been refined, and the metric system has been extended to incorporate many more units. Although a number of variants of the metric system emerged in the late nineteenth and early twentieth centuries, the term is now often used as a synonym for "SI" or the "International System of Units"—the official system of measurement in almost every country in the world.

The world map below shows the countries in green that have officially adopted the Metric System.

Measurement

When we measure we use a measuring tool to compare the specified dimension of an object to a standard. In every measurement there is a quantity (number) followed by units from the measuring device. A quantity does not have any meaning without the units.

For example, a person states that something weighs 21. It is left to you to interpret what the units are if they are not stated. They can be 21 ounces, 21 pounds, 21 kilograms; but you can never be sure. You can guess what the units would be by knowing what the person is measuring, but it is still a guess. However, if someone told you that something weighs 21 pounds, then you get a much clearer picture. The same is true for other units of measurement.

Writing the units after the number also falls under good documentation practices.