Units and Standards
The need for units and standards developed at a point in human history when people needed to know how much of something they were buying, selling, or exchanging. A farmer might want to sell a bushel of wheat, for example, for 10 dollars, but he or she could do so only if the unit "bushel" was known to potential buyers. Furthermore, the unit "bushel" had to have the same meaning for everyone who used the term.
The measuring system that most Americans know best is the British system, with units including the foot, yard, second, pound, and gallon. The British system grew up informally and in a disorganized way over many centuries. The first units of measurement probably came into use shortly after 1215. These units were tied to easily obtained or produced standards. The yard, for example, was defined as the distance from King Henry II's nose to the thumb of his outstretched hand.
The British system of measurement consists of a complex, irrational collection of units whose only advantage is its familiarity. As an example of the problems it poses, the British system has three different units known as the quart. These are the British quart, the United States dry quart, and the United States liquid quart. The exact size of each of these quarts differs.
In addition, a number of different units are in use for specific purposes. Among the units of volume in use in the British system, (in addition to those mentioned above) are the bag, barrel (of which there are three types—British and United States dry, United States liquid, and United States petroleum), bushel, butt, cord, drachm, firkin, gill, hogshead, kilderkin, last, noggin, peck, perch, pint, and quarter.