Systems of measurement are various sets of units used as standardized measurements of volume, weight, length, or flow. In ancient times, within a given community, measurements were simple, locally agreed upon units and often specific to the item being measured - a stride, a foot, a furlong; and bushel or peck for produce but pound or stone for all other other dry measurements.
Eventually, as trade more frequently crossed boarders, standardization across similar units was needed.
- inch, foot, mile for all distances
- ounce, pint, quart, gallon for all volumes
- ounce, pound, ton for all weights.
However, these ancient measurements can have an irregular and sometimes confusing relationship to each other. For example,
12 inches to 1 foot, 3 feet to 1 yard, and 1760 yards to 1 mile.
Eventually, around the time of the French Revolution, a simpler, more easily understood unit system based on 10 was devised using base units that could be expanded either smaller or larger: meter - length, gram - weight, liter - volume, and centigrade - temperature.
This system is called the International System, abbreviated SI for the French, Systeme International. Each base unit is expanded by multiplying or dividing the unit by factors of 10. Units that measure larger than the base unit are deca (x10), hecto (x100), kilo (x1,000), Mega (x1,000,000). Units that measure smaller than the base are milli (x0.1), centi (x0.01), deci (x0.001).
The centigrade temperature scale is based on dividing the the difference between ice and boiling water by 100. The International System spread throughout most of world today. Only 3 countries currently do not officially recognize this decimal (base 10) system: Burma, Liberia, and United States and even with in these countries the International System is used in combination with their own local systems.
US Customary System
The United States use a standardized version of the more ancient systems. It came over with the first colonists as it was the standard system in England at the time. It is familiar and normal for those who grow up with it.
This system uses inches, feet, yards, and miles for distance; ounces, cups, pints, quarts, gallons for volume; Fahrenheit for temperature; and ounces, pounds, and tons for weight. However our money system is decimal and things that are scientific in nature are defined by the decimal system
The US Customary is based on the older British system. The Imperial System is a British system that adjusted it's older cutomary system to more closely resemble the, then emerging, International System. It is a compromise between two systems that is still used today, although much of the United Kingdom now uses the International System.