The extension question from the E-Learning exercise

Extension:

Some units are no longer in used. Research on ONE of these old but interesting units of measurement and write a short paragraph on
i) its origin
ii) its relation to the SI unit
iii) its usefulness / advantages / disadvantages over the other units

ounce foot gallon dyne horsepower
inch league yard acre pound
or any other interesting units

Web References:
http://www.unc.edu/~rowlett/units/index.html
http://www.ex.ac.uk/cimt/dictunit/dictunit.htm#refs)

INCH
An inch is 2.54 centimeters. The origin of the inch is disputed. Historically, in different parts of the world (even different cities within the same country) and at different points in time, the inch has referred to similar but different standard lengths.
The English word inch comes from Latin uncia meaning "one twelfth part" (in this case, one twelfth of a foot); the word ounce (one twelfth of a troy pound) has the same origin.
In some other languages, the word for "inch" is similar to or the same as the word for "thumb"; for example, French: pouce inch/thumb; Italian: pollice inch/thumb; Spanish: pulgada inch, pulgar thumb; Portuguese: polegada inch, polegar thumb; Swedish: tum inch, tumme thumb; Danish: tomme inch, tommel thumb; Dutch: duim inch/thumb; Sanskrit: angulam inch, anguli finger; Slovak: palec inch/thumb; Hungarian: hüvelyk inch/thumb.
Given the etymology of the word "inch", it would seem that the inch is a unit derived from the foot, but this was probably only so in Latin and in Roman times. In English, there are records of fairly precise definitions for the size of an inch (whereas the definitions for the size of a foot are probably anecdotal), so it seems that the foot was then defined as 12 times this length. For example, the old English ynche was defined (by King David I of Scotland in about 1150) as the width of an average man's thumb at the base of the nail, even including the requirement to calculate the average of a small, a medium, and a large man's measures. To account for the much larger length later called an inch, there are also attempts to link it to the distance between the tip of the thumb and the first joint of the thumb, but this may be speculation.
There are records of the unit being used circa AD 1000 (both Laws of Æthelberht and Laws of Ælfred).
The unit of measurement “inch” can be used to measure larger objects more easily but for a more refined and accurate measurement of smaller objects the centimeter and millimeter are better. However the inch can also be used to facilitate easier approximations.
An inch is 0.0254 meters (2.54 centimeters).