#metric_grain__grain  used for pearls or diamonds: 50 mg or 1/4 carat
  supertype:  #metric_weight_unit__weight_unit  a decimal unit of weight based on the gram
  part of:  #decigram
  part:  #milligram__mg  1/1000 gram
     part:  #microgram__mcg  one millionth of a gram

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