code: def _make_units(*units):
      
  
      units_map = {}
      for value, names in units:
          units_map[value] = names[0]
          for name in names:
              units_map[name] = value
  
      return units_map
docs: Units map helper.  Each argument is treated as a unit
      descriptor--a tuple where the first element specifies a numerical
      value, and the second element consists of a sequence of names for
      that value.  Returns a dictionary where each name is mapped to the
      numerical value, and the numerical value is mapped to the first
      name.