Nano is a unit prefix meaning "one billionth". Used primarily with the metric system, this prefix denotes a factor of 10⁻⁹ or 0.000000001. It is frequently encountered in science and electronics for prefixing units of time and length. • One nanometer is about the length that a fingernail grows in one second. • Three gold atoms lined up are about one nanometer long. • If a toy marble were scaled down to one nanometer wide, Earth would scale to about 1 meter wide. • One nanosecond is about the time required for light to travel 30 cm in air, or 20 cm in an optical fiber. The prefix derives from the Greek νᾶνος, meaning "dwarf". The General Conference on Weights and Measures officially endorsed the usage of nano as a standard prefix in 1960. When used as a prefix for something other than a unit of measure, nano refers to nanotechnology, or means "on a scale of nanometres".