Meter bars were constructed first in brass and then in platinum to be used as references. Over the years, the definition of the meter changed several times to reflect the need for more accuracy. In 1906 and again in 1960 the meter was defined in terms of the wavelength of light. Throughout all these definition changes, the length of the meter has not changed, but the precision by which it is measured has improved.
Volume is derived from length.
The unit of volume is the cubic meter. A smaller, more convenient unit is the cubic decimeter, a cube measuring 10 centimeters on a side. The kilogram is the basic unit of mass. Although now fundamental, the kilogram was originally derived from volume. A kilogram was first defined as the mass of a cubic decimeter of water.