Triple Diamond calls are (4 or less)-dancer calls,
  requiring you to work only with the dancers in your Diamond.  For historical
  reasons, some callers use 8-dancer calls such
  as Diamond Chain Thru.  In this case, each dancer must select one of the
  other Diamonds to work with.  This is accomplished by selecting the Diamond
  nearest you or, if you are equidistant from both Diamonds, select the Diamond
  you are facing.  In today's nomenclature, the use of 8-dancer calls from
  Triple Diamonds should be given as '
Triple Diamonds Working
  Together...' 
EN: 50