The kilometer (from the Greek word for “thousand”) is a unit of length, equal to 1000 meters. It was first proposed in 1875 by the French scientist Georges Le Verneur, and was first used in 1880. The SI base unit of measurement is the meter, but since 2006, the kilometer has been recognized as an official unit of measure by the General Conference on Weights and Measures (CGPM), alongside the meter, kilogram and second. The kilometer is not officially defined, but it is based on the distance that light travels in a vacuum in 1/299.792 of a second.

The inch is a commonly used length unit in the United States and many other countries. An inch is equal to 0.00039 meters. The inch was originally a Roman unit of length, equal to 1/12 of a foot. It became an SI unit in the early 19th century, and is now one of the six standard lengths interdependent with meters (along with meter, kilometer, millimeter, micro meter, and nano meter). In 1935, theUSEb added the “point” to the name of the inch; thus 0.0003936 meters becomes 3.62 points, or 1/32nd of an inch.