The S.I. unit of length is meter (m). The 17th General Conference on Weights and Measures (CGPM), 1983 has defined the meter as: "The meter is the length of the path traveled by light in vacuum during a time interval of 2997924581 of a second." Sub units of meter: (1) centimeter (cm), (2) millimeter (mm), (3) micrometer (μm) or micron, (4) nanometer (nm)
Basics of standard unit of measurement
In ancient India length was measured using hand, muthi, fist etc, but measurement from it is not accurate, hence French created a standard unit of measurement called the metric system. Metric System is further classified to SI system (Standard International System) and CGS (centimeter, gram and second system). Foreg : In SI system,unit of length is metre denoted by "m" and 1m has 100 division. 1division =1cm(centimeter), which is the unit of length in CGS system.