
 The Unified Code for Units of Measure 
  The second is a metric unit because it is a part of the SI basis, although it used to be part of a series of customary units (originating in the Babylonian era). 
  The semantics of The Unified Code for Units of Measure is defined by the algebraic operations of multiplication, division and exponentiation between units, by the equivalence relations of equality and commensurability of units, and by the multiplication of a unit with a scalar. 
  Units were taken from nature: anatomical structures (e.g., arm, foot, finger), botanical objects (e.g., grains of various sorts, rod), or processes of everyday life (e.g., amount of land one could plow in a morning, the length of 1000 steps, an hour of walking, etc.). 
 aurora.rg.iupui.edu /~schadow/units/UCUM/ucum.html (8920 words) 
