The Correlation of Units
National Metric Week

In the United States, there are still ongoing efforts to get Americans onboard with standardized measurements, and one of those is National Metric Week. In 2011, it's celebrated the week of Oct. 9 to Oct. 15 -- set in the 10th month of the year, and inclusive of the 10th day of that month.

The units for different types of measures -- such as length and volume -- correlate with one another. For example, 1 milliliter (a unit of volume) has the same proportions as 1 cubic centimeter (centimeters being a measure of length). A liter of water, by extension, is the equivalent of 1 cubic decimeter. It also has a mass approximately the same as 1 kilogram. This even works by expansion; 1 cubic meter can hold approximately 1,000 liters of water and has about the same mass as 1 metric ton -- or 1,000 kilograms.

And apart from the seven base units in the metric system -- the meter, the kilogram, the second, the ampere, the kelvin, the mole and the candela -- other meaningful units of measurement can be derived from those. Consider velocity. It's typically denoted by a unit of length (kilometers) divided by a unit of time (hours).